





By 


-^S SjASSIFTRn 

authority Secretary of 

2 6 1960 


Defense memo 2 August I960 

dibkaky op congress 



^OCUtosST, ALL CLASaj^f^^ THIS 


S£i£- 










SUMMARY TECHNICAL REPORT 
OF THE 

NATIONAL DEFENSE RESEARCH COMMITTEE 


This document contains information affecting the national defense of 
the United States within the meaning of the Espionage Act, 50 U. S. C., 
31 and 32, as amended. Its transmission or the revelation of its contents 
in any manner to an unauthorized person is prohibited by law. 

This volume is classified^H^Bl^ in accordance with security regula- 
tions of the War and Navy De partm ents because certain chapters 
contain material which was the date of printing. Other 

chapters may have had a lower classification or none. The reader is 
advised to consult the War and Navy agencies listed on the revei'se 
of this page for the current classification of any material. 


Manuscript and illustrations for this volume were prepared 
for publication by the Summary Reports Group of the 
Columbia University Division of War Research under con- 
tract OEMsr-1131 with the Office of Scientific Research and 
Development. This volume was printed and bound by the 
Columbia University Press. 

Distribution of the Summary Technical Report of NDRC 
has been made by the War and Navy Departments. Inquiries 
concerning the availability and distribution of the Summary 
Technical Report volumes and microfilmed and other refer- 
ence material should be addressed to the War Department 
Library, Room lA-522, The Pentagon, Washington 25, D. C., 
or to the Office of Naval Research, Navy Department, Atten- 
tion : Reports and Documents Section, Washington 25, D. C. 

Copy No. 

238 


This volume, like the seventy others of the Summary Tech- 
nical Report of NDRC, has been written, edited, and printed 
under great pressure. Inevitably there are errors which have 
slipped past Division readers and proofreaders. There may 
be errors of fact not known at time of printing. The author 
has not been able to follow through his writing to the final 
page proof. 

Please report errors to : 

JOINT RESEARCH AND DEVELOPMENT BOARD 
PROGRAMS DIVISION (STR ERRATA) 

WASHINGTON 25, D. C. 

A master errata sheet will be compiled from these reports 
and sent to recipients of the volume. Your help will make 
this book more useful to other readers and will be of great 
value in preparing any revisions. 


SUMMARY TECHNICAL REPORT OF DIVISI 



VOLUME 1 


2 6 1960 

RADAR: SUMMARY 

AND HARP PROJECT 


OFFICE OF SCIENTIFIC RESEARCH AND DEVELOPMENT 
VANNEVAR BUSH, DIRECTOR 

NATIONAL DEFENSE RESEARCH COMMITTEE 
JAMES B. CONANT, CHAIRMAN 

DIVISION 14 
A. L. LOOMIS, CHIEF 


WASHINGTON, D.C., 1946 



NATIONAL DEFENSE RESEARCH COMMITTEE 


James B. Conant, Chairman 
Richard C. Tolman, Vice Chairman 
Roger Adams Army Representative^ 

Frank B. Jewett Navy Representative^ 

Karl T. Compton Commissioner of Patents^ 

Irvin Stewart, Executive Secretary 


^Army Representatives in oi'der of service : 
Maj. Gen. G. V. Strong Col. L. A. Denson 

Maj. Gen. R. C. Moore Col. P. R. Faymonville 

Maj. Gen. C. C. Williams Brig. Gen. E. A. Regnier 
Brig. Gen. W. A. Wood, Jr. Col. M. M. Irvine 
Col. E. A. Routheau 


'^Navy Representatives in order of service: 

Rear Adm. H. G. Bowen Rear Adm. J. A. Purer 

Capt. Lybrand P. Smith Rear Adm. A. H. Van Keuren 

Commodore H. A. Schade 
^Commissioners of Patents in order of service: 
Conway P. Coe Casper W. Ooms 


NOTES ON THE ORGANIZATION OF NDRC 


The duties of the National Defense Research Committee 
were (1) to recommend to the Director of OSRD suitable 
projects and research programs on the instrumentalities 
of warfare, together with contract facilities for carrying 
out these projects and programs, and (2) to administer 
the technical and scientific work of the contracts. More 
specifically, NDRC functioned by initiating research 
projects on requests from the Army or the Navy, or on 
requests from an allied government transmitted through 
the Liaison Office of OSRD, or on its own considered 
initiative as a result of the experience of its members. 
Proposals prepared by the Division, Panel, or Committee 
for research contracts for performance of the work in- 
volved in such projects were first reviewed by NDRC, and 
if approved, recommended to the Director of OSRD. Upon 
approval of a proposal by the Director, a contract permit- 
ting maximum flexibility of scientific effort was arranged. 
The business aspects of the contract, including such 
matters as materials, clearances, vouchers, patents, pri- 
orities, legal matters, and administration of patent mat- 
ters were handled by the Executive Secretary of OSRD. 

Originally NDRC administered its work through five 
divisions, each headed by one of the NDRC members. 
These were: 

Division A — Armor and Ordnance 
Division B — Bombs, Fuels, Gases, & Chemical Problems 
Division C — Communication and Transportation 
Division D — Detection, Controls, and Instruments 
Division E — Patents and Inventions 


In a reorganization in the fall of 1942, twenty-three 
administrative divisions, panels, or committees were 
created, each with a chief selected on the basis of his 
outstanding work in the particular field. The NDRC mem- 
bers then became a reviewing and advisory group to the 
Director of OSRD. The final organization was as follows: 

Division 1 — Ballistic Research 

Division 2 — Effects of Impact and Explosion 

Division 3 — Rocket Ordnance 

Division 4 — Ordnance Accessories 

Division 5 — New Missiles 

Division 6 — Sub- Surface Warfare 

Division 7 — Fire Control 

Division 8 — Explosives 

Division 9 — Chemistry 

Division 10 — Absorbents and Aerosols 

Division 11 — Chemical Engineering 

Division 12 — Transportation 

Division 13 — Electrical Communication 

Division 14 — Radar 

Division 15 — Radio Coordination 

Division 16 — Optics and Camouflage 

Division 17 — Physics 

Division 18 — War Metallurgy 

Division 19 — Miscellaneous 

Applied Mathematics Panel 

Applied Psychology Panel 

Committee on Propagation 

Tropical Deterioration Administrative Committee 



NDRC FOREWORD 


AS EVENTS of the years preceding 1940 revealed 
more and more clearly the seriousness of 
the world situation, many scientists in this 
country came to realize the need of organizing 
scientific research for service in a national emer- 
gency. Recommendations which they made to the 
White House were given careful and sympathetic 
attention, and as a result the National Defense 
Research Committee [NDRC] was formed by 
Executive Order of the President in the summer 
of 1940. The members of NDRC, appointed by 
the President, were instructed to supplement the 
work of the Army and the Navy in the develop- 
ment of the instrumentalities ofwar. A year later, 
upon the establishment of the Office of Scientific 
Research and Development [OSRD], NDRC 
became one of its units. 

The Summary Technical Report of NDRC is 
a conscientious effort on the part of NDRC to 
summarize and evaluate its work and to present 
it in a useful and permanent form. It comprises 
some seventy volumes broken into groups cor- 
responding to the NDRC Divisions, Panels, and 
Committees. 

The Summary Technical Report of each Divi- 
sion, Panel, or Committee is an integral survey 
of the work of that group. The first volume of 
each group's report contains a summary of the 
report, stating the problems presented and the 
philosophy of attacking them, and summarizing 
the results of the research, development, and 
training activities undertaken. Some volumes 
may be ‘‘state of the art" treatises covering sub- 
jects to which various research groups have con- 
tributed information. Others may contain de- 
scriptions of devices developed in the labora- 
tories. A master index of all these divisional, 
panel, and committee reports which together 
constitute the Summary Technical Report of 
NDRC is contained in a separate volume, which 
also includes the index of a microfilm record of 
pertinent technical laboratory reports and ref- 
erence material. 

Some of the NDRC-sponsored researches 
which had been declassified by the end of 1945 
were of sufficient popular interest that it was 
found desirable to report them in the form of 
monographs, such as the series on radar by 
Division 14 and the monograph on sampling 
inspection by the Applied Mathematics Panel. 


Since the material treated in them is not dupli- 
cated in the Summary Technical Report of 
NDRC, the monographs are an important part 
of the story of these aspects of NDRC research. 

In contrast to the information on radar, 
which is of widespread interest and much of 
which is released to the public, the research on 
subsurface warfare is largely classified and is 
of general interest to a more restricted group. 

As a consequence, the report of Division 6 is 
found almost entirely in its Summary Technical 
Report, which runs to over twenty volumes. The 
extent of the work of a Division cannot therefore 
be judged solely by the number of volumes de- 
voted to it in the Summary Technical Report of 
NDRC: account must be taken of the mono- 
graphs and available reports published else- 
where. 

To A. L. Loomis, Chief of Division 14, the men 
who worked under his direction, and the person- 
nel of the Division’s contractors belongs major 
credit for the perfection of a device which force- 
fully altered the course of the war. The applica- 
tion of radar by all Services in all theaters of > 
operation is an eloquent testimonial not only to 
the skill of these men but also to their will, their 
loyal cooperation, and their scientific integrity. 

The Summary Technical Report of the Division, 
prepared under the direction of the Division 
Chief and authorized by him for publication, 
therefore not only describes a major portion of 
their technical activities but is also a record of 
able American scientists and engineers cooper- 
ating fully in the defense of their country. 

It is assuring to know that their contributions 
in the new field of microwaves will not be placed 
in intellectual cold storage to await purely mil- 
itary applications, but instead will soon find use 
in the industry, the transportation, the com- 
munications, and the scientific researches of a 
peacetime world. 

For their work in opening a broad entrance 
to a new field of knowledge as well as for their 
invaluable contributions in a time of desperate 
strife, we join the Nation in expressing our 
sincere appreciation. 

Vannevar Bush, Director 

Office of Scientific Research and Development 
J. B. CoNANT, Chairman 
National Defense Research Committee 


V 



FOREWORD 


D ivision 14 of the National Defense Research 
Committee was responsible for the micro- 
wave radar and Loran developments within the 
Office of Scientific Research and Development. 
Its original purpose, as defined at one of the early 
Division meetings, was “to organize and coordi- 
nate research, invention, design and manufacture 
in order to obtain the maximum number of effec- 
tive applications of microwaves in the minimum 
time.'’ Under this directive. Division 14 estab- 
lished and administered a total of 137 OSRD 
contracts with 18 academic and private research 
institutions, and 39 industrial concerns enter- 
ing into almost every phase of the country’s 
wartime radar program. The principal contract, 
accounting for approximately 80 per cent of the 
Division’s contract appropriations, was to the 
Massachusetts Institute of Technology Radia- 
tion Laboratory. This laboratory through con- 
tinuous growth and expansion of the scope of 
its activities became the center of microwave 
radar research and development effort. 

The success of the program was without ques- 
tion due to the close collaboration of the many 
participating agencies and institutions. Many 
of the country’s academic and industrial insti- 
tutions worked with the Radiation Laboratory 
in research and development programs under 
Army and Navy as well as OSRD contracts. 
Radio and electrical equipment manufacturers 
were responsible for final engineering and large 
scale production of components and systems. 
The Army and Navy carried out procurements 
planning, proof testing, training, and the elab- 
orate functions of supply and maintenance. 
Close technical liaison, furthermore, was main- 
tained throughout World War II with radar 
research organizations of the British Common- 
wealth of Nations. The contributions of the 
many participating organizations must be ac- 
knowledged by any single agency attempting 
to present its final report. 

The NDRC Summary Technical Report is 
intended to include the pertinent results of each 
Division’s program. The selection of material 
for such a report invariably presents a difficult 
problem. A choice must be made from the work 


of many organizations and individuals during 
a complex five-year program. 

The Division 14 Summary Technical Report 
consists of three volumes. The first. Radar, con- 
tains a summary of the Division 14 and Radia- 
tion Laboratory activities and selected project- 
reports, and appendices listing the Division’s 
projects and contracts. It is intended to serve 
as a general guide to the Division’s activities. 
Volume 2 of the Division 14 STR is entitled 
Military Airborne Radar Systems [MARS]. 
This volume is a detailed treatment of the de- 
sign, development, installation, maintenance, 
and performance of aircraft radar for such ap- 
plications as search, bombing, navigation, inter- 
ception, and fire control. The volume is intended 
as a general text for use by officers and civilian 
engineers concerned with almost any aspect of 
aircraft radar development, engineering, pro- 
curement, training, or operational use. Volume 
3 contains a complete bibliography of the con- 
tract and division reports prepared during the 
course of the program. 

The largest publication effort of Division 14 
is the Radiation Laboratory Series prepared by 
the MIT Radiation Laboratory for publication 
by the McGraw-Hill Book Company. This set of 
monographs is considered as a supplement to the 
Division 14 Summary Technical Report. It con- 
sists of some twenty-seven volumes and an index 
and is a complete report on the state of the radar 
art at the end of World War II, including texts 
on fundamental electronics, components and 
systems design and engineering, peacetime ap- 
plications, and Loran navigation. A list of the 
titles and an abstract of 'each book is contained 
in Volume 3. 

The progress and interim technical reports 
submitted by the MIT Radiation Laboratory 
and the other Division 14 contractors constitute 
valuable reference material on the division’s 
program. They cover specific aspects of the 
work and are not duplicated by the Summary 
Technical Report or the Radiation Laboratory 
Series. All of the approximately 2,000 of these 
reports have been indexed by report number, 
subject, organization, and, in the case of the 


vii 


viii 


FOREWORD 


Kadiation Laboratory reports, by author in the 
bibliography of Volume 3. Microfilm prints of 
these reports are available to those who have 
access to the Summary Technical Reports. 

Another category of reports which are in- 
cluded in the bibliography and microfilms are the 
Division 14 project reports. These were bi- 
monthly reports of activities to the Army and 
Navy. Included are pertinent technical details 
of the systems, projects, and summaries of the 
basic research and component development ac- 
tivities. The final project report, NDRC 14-565, 
dated December 1945, reviews the entire pro- 
gram of the Division. It contains an index of all 
Division 14 projects. Service Projects, with cross 
references to contracts and Army and Navy 
equipment designations. 

The history of Division 14 has been prepared 
and edited by H. E. Guerlac for publication with 
the other volumes of the OSRD history by the 
Little, Brown Company, Inc., Boston. It traces 
the early work on radar before the war by the 
Army, Navy, British, and various private insti- 
tutions, describes the origin of NDRC’s micro- 
wave development activities, the foundation of 
the Massachusetts Institute of Technology Ra- 
diation Laboratory and gives a historical sum- 
mary of the principal Division systems and com- 
ponents resulting from the research program. 
A final section that should be of general interest 
reports on the field service activities of the Divi- 
sion and the operational results obtained with 
several types of microwave radar equipment. 

This first volume of the Division 14 Summary 
Technical Report does not purport to review 
completely all Division 14 activities. Parts I and 
II give some of the highlights of the Division's 
program with comments on the administration 


of the Radiation Laboratory and its relation with 
industry and the government agencies concerned 
with the production and use of radar. They also 
tell the story of the Microwave Committee which 
preceded Division 14 and of the establishment 
and organization of the Radiation Laboratory 
program. The volume also contains a brief de- 
scription of the principal Division 14 projects. 
One section is devoted to the magnetron develop- 
ments of the Columbia University Radiation 
Laboratory. However, it has not been possible to 
cover more than a few major projects of the 
Division. 

Part III, '‘Harp, Material with Artificially 
Constructed Dielectric Constant and Permea- 
bility,” reports on a new material development 
project at the Laboratory for use in radar cam- 
ouflage, identification systems, and other special 
applications. The article was not included in the 
Radiation Laboratory Series for security rea- 
sons. 

Two important publications which were origi- 
nally intended for inclusion in the Division 14 
Summary Technical Report were deleted and 
arrangements made for their publication else- 
where. They are Development of Cadillac Air- 
borne Early Warning Systems, C. J. Kelly, Field 
Station, Naval Research Laboratory , Boston, and 
The Gun Fire-Control System, Mark 56, Navy 
Publication OP-1600 E. 

I should like to express my appreciation to the 
authors, L. A. DuBridge, H. E. Guerlac, M. H. 
Johnson, 0. Halpern, and to the other members 
of the Radiation Laboratory and Division 14 
staff who assisted in the preparation of this 
^volume. 

A. L. Loomis, 
Chief, Division 14 






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TITLES OF DIVISION 14 SUMMARY TECHNICAL REPORTS 


SUMMARY TECHNICAL REPORT OF DIVISION 14, NDRC 

Volume 1 Radar: Summary Reports and Harp Project 
Volume 2 Military Airborne Radar Systems (MARS) 

Volume 3 Bibliography of Division 14 and Radiation 
Laboratory Reports 

RADIATION LABORATORY SERIES 
(Published by the McGraw-Hill Book Company) 

1. Radar System Engineering, Louis N. Ridenour 

2. Radar Aids to Navigation, J. S. Hall 

3. Radar Beacons, A. Roberts 

4. Loran, J. a. Pierce, A. A. McKenzie, R. H. Woodward 

5. Pulse Generators, G. N. Glasoe, J. V. Lebacqz 

6. Microwave Magnetrons, George B. Collins 

7. Klystrons and Microwave Triodes, D. R. Hamilton, J. K. Knipp, 

J. B. H. Kuper 

8. Principles of Microwave Circuits, C. G. Montgomery, E. M. Purcell, 
R. H. Dicke 

9. Microwave Transmission Circuits, G. L. Ragan 

10. Waveguide Handbook, N. Marcuvitz 

11. Technique of Microwave Measurements, C. G. Montgomery 

12. Microwave Antenna Theory and Design, S. Silver 

13. Propagation of Short Radio Waves, D. E. Kerr 

14. Microwave Duplexers, L. D. Smullin, C. G. Montgomery 

15. Crystal Rectifiers, H. C. Torrey, C. A. Whitmer 

16. Microwave Mixers, R. V. Pound 

17. Components Handbook, John F. Blackburn 

18. Vacuum Tube Amplifiers, George E. Valley, Jr., Henry Wallman 

19. Waveforms, Britton Chance, F. C. Williams, V. W. Hughes, D. Sayre, 
E. F. MacNichol, Jr. 

20. Electronic Time Measurements, Britton Chance, R. I. Hulsizer, 

E. F. MacNichol, Jr. 

21. Electronic Instruments, I. A. Greenwood, Jr., D. MacRae, Jr., 

H. J. Reed, J. V. Holdam, Jr. 

22. Cathode Ray Tube Displays, J. T. Seller, M. A. Starr, 

George E. Valley, Jr. 

23. Microwave Receivers, S. N. VanVoorhis 

24. Threshold Signals, J. L. Lawson, G. E. Uhlenbeck 

25. Theory of Servomechanisms, H. M. James, N. B. Nichols, 

R. S. Phillips 

26. Radar Scanners and Radomes, W. M. Cady, M. B. Karelitz, 

L. A. Turner 

27. Computing Mechanisms and Linkages, A. Svoboda 

28. Index 


CONTENTS 


PART I 

HISTORY AND ORGANIZATION OF 

CHAPTER RADAR ACTIVITIES page 

1 Summary 3 

2 The Origin of Microwave Radar and Loran Navigation 

Developments in the NDRC 25 

PART II 

PROGRAM OF RADIATION LABORATORY 
AND ASSOCIATES 

3 Technical Program of the Radiation Laboratory ... 39 

4 The Columbia Radiation Laboratory 55 

5 Selected Ground Systems Projects 63 

6 Aircraft Radar Systems 71 

7 Ship Systems 85 

8 Project Cadillac, Airborne Early-Warning Radar Systems . 89 

PART III 

HARP— MATERIAL WITH ARTIFICIALLY CONSTRUCTED 
DIELECTRIC CONSTANT AND PERMEABILITY 

9 Development and Production Processes 99 

10 Electromagnetic Properties of HARP 105 

11 Theory and Applications of Resonant Absorbent Layers . 109 

12 Technical Applications of HARP 129 

Glossary 139 

Bibliography 145 

OSRD Appointees 147 

Contract Numbers 148 

Service Project Numbers 154 

Index 163 



PART I 


HISTORY AND ORGANIZATION 
OF RADAR ACTIVITIES 



\ 


Chapter 1 

SUMMARY 


1.1 INTRODUCTION 

I N JUNE 1940 Dr. K. T. Compton, chairman of 
Division D of the National Defense Research 
Committee [NDRC], established a section to 
study the applications of microwaves (radio 
waves less than 5 in. long) to military detection 
devices. This Section D-1 was headed by Alfred 
L. Loomis, and he eventually called in as mem- 
bers a group of a dozen university and indus- 
trial scientists and engineers. Known popularly 
as the Microwave Committee, the section con- 
tinued, with remarkably few changes in person- 
nel, throughout the war, later becoming Division 
14 (Radar) of NDRC. 

During the summer of 1940 members of this 
committee investigated the radio-detection de- 
velopments (now known as “radar”) which were 
being carried on under the supervision of the 
Army and Navy in this country. During this 
investigation they became impressed with the 
fact that it would be of great importance if 
microwave techniques could be developed and 
applied to radio-detection equipment. A small 
group of physicists and engineers worked dur- 
ing the summer of 1940 at the Loomis Labora- 
tories, in Tuxedo Park, New York, exploring 
methods of generating, detecting and using 
microwaves. Excellent progress in the explora- 
tion of microwave techniques was made, but the 
results on the whole were discouraging because 
of the fact that no vacuum tube was available 
which would generate microwave pulses suffi- 
ciently intense for practical pulse-detection 
equipment. 

Report of the British Technical 
Mission 

In the early fall of 1940, a British Technical 
Mission, headed by Sir Henry Tizard, arrived in 
this country bringing to Army, Navy, and NDRC 
officials the full story of the development and use 
of radar equipment in England. This Mission 
revealed the critical importance of such equip- 
ment in modern warfare and requested the co- 


operation of the United States in the develop- 
ment effort. Its members also revealed that a 
group at the University at Birmingham had de- 
veloped a new form of cavity magnetron which 
was capable of generating pulses of 10-kw peak 
power at a frequency of 3,000 me, or 10-cm wave- 
length. 

The availability of this single device opened 
up the whole field of microwave radar, and the 
Microwave Committee at once realized the pos- 
sibilities and importance of developing this new 
field. 

In addition, the British mission had brought 
the information that the most urgently needed 
radio-detection equipment was a set which could 
be installed in a night-fighter airplane to effect 
night interceptions of enemy bombers. The Brit- 
ish laboratories had outlined the general require- 
ments and specifications for such an equipment, 
and calculations had shown that with the new 
magnetron a set sufficiently powerful to detect 
enemy aircraft at 3 or 4 miles would be feasible. 

The U. S. Army Air Forces were keenly inter- 
ested in this proposal and joined the British in 
requesting NDRC to undertake the development 
of microwave aircraft interception [AI] equip- 
ment. 

1.1.2 MIT Radiation Laboratory 

The Microwave Committee at once decided to 
follow the British pattern and set up a special 
laboratory, manned by physicists and engineers, 
to carry forward at a rapid rate this specific 
development. 

After investigating several possibilities, the 
committee members came to the conclusion that 
the Massachusetts Institute of Technology 
[MIT] offered the only feasible location for such 
a laboratory, and the MIT administration was 
persuaded to provide the necessary space and 
facilities. 

A group of physicists from universities was 
at once recruited, and several members of the 
staff of the Department of Electrical Engineer- 
ing of MIT who had been working at the Loomis 


3 


4 


SUMMARY 


Laboratories during the summer were trans- 
ferred to the new MIT laboratory. This group 
of about twenty-five men began active work in 
November 1940. 

In the meantime Dr. E. G. Bowen, a member 
of the British mission, had outlined to the Micro- 
wave Committee the proposed specifications of 
the projected AI equipment. The Microwave 
Committee, in order to have equipment and ma- 
terials ready for use in the laboratory, had given 
contracts to several industrial laboratories for 
the development and manufacture of several 
models of each of the major components of the 
proposed system (magnetron, pulser, antenna, 
receiver, and indicator) . Thus, in the first days 
of the laboratory, the basis had been laid for 
intimate collaboration between it and indus- 
trial laboratories which continually expanded 
throughout the life of the laboratory. 

1940 Developments 

Within a few days after they assembled the 
members of the new laboratory, who decided to 
call themselves the Radiation Laboratory [RL] , 
were at work studying microwave techniques 
and learning from Dr. Bowen the military and 
technical problems involved in AI equipment. 
Dr. Bowen was an extremely fortunate choice 
for the position of British liaison officer at the 
laboratory. His long experience under Sir Robert 
Watson-Watt on radio-detection problems and 
his intimate contact with the RAF and its mili- 
tary problems made him the chief source of in- 
formation for MIT-RL in its early days. His wide 
knowledge and his charming personality quickly 
won the admiration and respect of the laboratory 
members, and he exerted a profound influence 
in the formulation of MIT-RL plans. 

Experimental Models 

Work on the components of the first experi- 
mental microwave system began immediately 
and by the end of 1940, the first U. S. microwave 
pulse radar system was ready for operation. 
Crude as the system was by present standards, 
it was a remarkable achievement in that it was 
put together, starting from scratch, within 
about two months. In that two months^ period, 
also, some of the major components of the first 
airborne set were well under way, and it was 


assembled and ready for test by January 1941. 
In the meantime negotiations with the Army 
carried out largely by E. L. Bowles, then Secre- 
tary of the Microwave Committee, resulted in 
the formulation of plans for the supply of an 
experimental airplane for laboratory use and 
for the installation of additional AI sets in other 
planes. In fact, by the beginning of 1941, the 
laboratory was already making plans for its first 
“crash'' program, namely, the building in the 
laboratory of fifteen AI sets for the early ex- 
perimental models of the P-61 airplane. 

Antiaircraft Models 

Within the first two months of its existence, 
MIT-RL had undertaken two additional projects 
which had been planned by the Microwave Com- 
mittee. The first was a microwave radar of high 
precision for use with antiaircraft guns. Dr. 
Loomis had proposed the development of the 
principle of conical scan, which later proved so 
successful, and a small group was at work study- 
ing the problems of radar fire control. 

Loran 

The third project was that of long-range navi- 
gation (later called “Loran"), the scheme for 
which had been outlined by Dr. Loomis. A spe- 
cial committee of Section D-1, under the chair- 
manship of Dr. Ralph Bowen of the Bell Tele- 
phone Laboratories [BTL], supervised various 
industrial contracts and helped organize the 
work on this project. 

The end of the year 1940, therefore, saw the 
laboratory embarked on an intense program 
with a thriving and capable group of some 75 
men, working day and night, laying the basis for 
the great program which was yet to come but was 
still only dimly foreseen. There was, at that time, 
some feeling that nine to twelve months of work 
would see the basic microwave research com- 
pleted, and the group would then disband. But 
this was a year before the United States entered 
the war, and it was before the enormous possi- 
bilities of microwave radar were dreamed of. 

1.2 1941— EXPLORATION 

Performance of First Models. The year 1941 
was a momentous one in the microwave art and 
in MIT-RL history. The laboratory continued to 


1941— EXPLORATION 


5 


expand throughout the year, and its personnel 
nearly reached the 500 mark by the year’s end. 
Early in the year the need for much more space 
than could be provided within MIT buildings was 
visualized, and plans were laid for the construc- 
tion of a permanent building. 

The technical development work proceeded 
with remarkable rapidity. The first experimental 
radar system operated successfully in January, 
and its performance improved by leaps and 
bounds during the succeeding weeks. The first 
system designed for aircraft installation was op- 
erating in early February, and on February 7 
tracked a small plane to a distance of 21/2 miles. 
This was the first confirmation that a microwave 
AI system was practically feasible. By March the 
range had improved to 5 miles, at which time 
the system was installed in a B-18 airplane sup- 
plied by the Army. In the meantime lighter and 
improved systems were under way. By the mid- 
dle of the year the Army had placed a contract 
for such equipment with the Western Electric 
Company, and a laboratory experimental set was 
taken to the Bell Telephone Laboratories [BTL] 
along with two RL men, who assisted in working 
out the production design. The laboratory as- 
sisted in general development of components of 
the AI-10 after this time, but BTL carried the 
responsibility for further development of Army 
10-cm AI equipment from that time forward. 
Eventually this development resulted in the ex- 
tremely successful SCR-720, which was used ex- 
tensively by the British and American Air 
Forces. 

High-Frequency Magnetron Development, 
Many new microwave problems were springing 
up, however, each month. Almost from the outset 
the development of higher-frequency magne- 
trons was a part of the research program. Col- 
laborating with BTL and the Raytheon Manu- 
facturing Company, the magnetron group had 
3-cm magnetrons under test by March, and the 
laboratory was already visualizing an AI set 
using this new higher frequency which would 
allow much greater compactness in airborne in- 
stallations. The U. S. Navy soon became inter- 
ested in this possibility since it was concerned 
with carrier-based aircraft. By the end of 1941 
designs of the preliminary Navy AIA were well 
under way. 


Plan-Position Indicator. Flight tests with the 
AI-10 equipment had shown its great value in 
detecting surface vessels when flying over the 
sea. The first airborne plan-position indicator 
[PPI] was developed to improve the perform- 
ance of equipment for this purpose, and micro- 
wave air craft-to-sur face vessel [ASV] equip- 
ment was successful almost from the start. With 
the submarine war growing in intensity, the 
British were keenly interested in this develop- 
ment, and by the end of the year experimental 
equipment was being made for trials in England. 

Fire-Control Radar. The development of 10- 
cm fire-control radar proceeded rapidly and in 
March the first automatic-tracking microwave 
radar was in operation on the roof laboratory of 
MIT. The accuracy and reliability of tracking 
was sufficiently great, even with the experi- 
mental equipment, to attract the interest of the 
Coast Artillery Board, then responsible for anti- 
aircraft gunnery. With its interest expressed, a 
mobile automatic-tracking unit installed in a 
truck (the famous XT-1) was ready for trials by 
the end of the year. This represented a particu- 
larly extraordinary achievement since precision, 
field reliability, and elaborate data-transmission 
mechanisms had to be designed in addition to the 
basic radar equipment. The basic soundness of 
the early design was exhibited by the fact that 
the production models, which essentially copied 
it, were still, in 1945, among the best and most 
versatile ground radar equipments available in 
the field. 

Shipborne Radar. Another major step was 
taken in 1941 when equipment originally de- 
signed for aircraft installation was modified and 
installed aboard a U. S. Navy destroyer, USS 
Semmes. This was the first microwave radar 
with PPI presentation to be used on shipboard, 
and the first tests showed the great value which 
such a shipborne radar would have. Naval offi- 
cers were so impressed that by the summer of 
the year a production order had been placed with 
Raytheon for what was later called the SG radar, 
one of the most widely used and successful of all 
shipboard radars. 

Harbor and Coastal Applications. A set some- 
what similar to that installed on the USS Semmes 
was installed in a truck for mobile field tests dur- 
ing the year. It was tried extensively at Deer 


6 


SUMMARY 


Island in Boston Harbor as a harbor surveillance 
set, primarily to collect data on the surface- 
search problem. When the United States entered 
the war in December, this experimental set was 
requested by the Boston Harbor Entrance Con- 
trol Station and was put at once into service as a 
day-and-night surveillance set for the Boston 
Harbor. At the same time the Signal Corps and 
the Coast Artillery requested the newly organ- 
ized Research Construction Company Model 
Shop to build fifty of these sets, designated as 
the SCR-582. This was a terrific order for a 
struggling young model shop to take, but after 
long consideration it was taken and the order 
successfully completed during 1942. These fifty 
sets saw extensive use in the field. 

Summary of 1941 Research 

These are only some of the major exploratory 
new systems which were developed during 1941. 
Radar for the control of aircraft armament, for 
range-finding, for shipboard machine guns, 
high-power search and height-finding equipment 
for interception control, and a number of other 
projects were initiated during the year. In each 
case the experimental microwave equipment was 
able to fill a totally new purpose or was superior 
to previous equipment. By the end of the year 
microwaves “were here to stay” and were not 
“something for the next war.” 

The rapid extension of application of micro- 
waves to military problems was accompanied by 
equally rapid development of the basic compo- 
nents of microwave radar. Compact pulsers for 
airborne use were developed; microwave re- 
ceiver design was enormously improved; TR 
boxes, waveguide and transmission-line tech- 
niques, antenna designs, and indicator designs 
all went through developments which resulted in 
very large improvements in performance and 
reliability. 

Although by the end of 1941 not a single micro- 
wave set was in combat use, the basis for the new 
industry had been laid, production orders for 
‘ many sets had been placed, and extensive trials 
had proved the value and versatility of micro- 
wave techniques. Thus in the space of a single 
year microwave radar had arrived and was 
ready to emerge from the laboratory. 


1.3 1942-EMERGING FROM THE 
LABORATORY 

Expansion of Facilities. The year 1942 wit- 
nessed the most remarkable fiowering of MIT- 
RL activities. This year saw microwave equip- 
ment brilliantly successful in combat use, saw a 
tremendous further flowering of the possibili- 
ties of application to new tactical problems, and 
witnessed further development and perfection of 
every microwave radar component. 

The problems laid out and planned in 1942 are 
those which occupied most of the laboratory’s 
attention for the rest of its existence. This year 
also witnessed the most rapid growth in scien- 
tific personnel in the laboratory’s history. The 
total personnel employed rose from 450 at the 
beginning of the year to 1,700 at the end. The 
new Building 24 was occupied and almost imme- 
diately expanded by the addition of five floors, 
and by the middle of the year a huge temporary 
building. Building 22, was occupied. 

Use in Submarine Warfare. The United States 
was now at war, and there were immediate per- 
sonnel reasons on the part of each member of the 
staff for pushing the work ahead rapidly and 
effectively. At the beginning of the year an im- 
mediate emergency arose with the disastrous 
success of the German submarines along the 
Atlantic Coast. The laboratory, in a rush job, 
converted parts intended for AI-10 equipments 
into ASV sets, and installed them in ten B-18 
planes which formed a coastal patrol squadron 
operating out of Langley Field. Almost at once 
these planes were successful in detecting and 
sinking German submarines, and they, with 
later planes equipped with production sets, 
played an exceedingly important role in even- 
tually eliminating the submarine menace from 
the coastal waters of the United States. 

This operational success served to redouble 
the efforts at MIT-RL. As the year went on, addi- 
tional operational successes multiplied. The Brit- 
ish were planning an intensive campaign against 
the U-boat in the Bay of Biscay, and for this they 
used much American equipment. American 
planes also participated in this campaign, which 
finally spelled the death of the U-boat as a threat 
to Allied success. 

By the middle of 1942 the MIT-RL had some 


1943— THE RISING TIDE 


7 


twenty system projects on its books, a number 
which had grown to nearly fifty by the end of the 
year. During the year, also, the production lines 
began turning out RL equipment in quantity, 
and by the end of the year many sets were in 
large-scale production. Laboratory-built sets, as 
well as production sets, were serving in many 
theaters of war by the end of the year. 

Production and Design Progress. Within MIT- 
RL many basic new ideas for microwave appli- 
cations were developed. The precision bombing- 
through-overcast equipment, known as Eagle, 
was mapped out and preliminary experiments 
begun. The first ideas for a long-range micro- 
tvave early -teaming [MEW] set, were laid down, 
as well as the fundamental principles of the 
ground control of approach [GCA], a set for 
landing aircraft under conditions of poor visi- 
bility. A considerable effort went into the devel- 
opment of airborne fire-control equipment, a 
field of great complexity because of the multi- 
plicity of types of airplanes and guns; 3-cm 
equipment for airborne and shipborne use de- 
veloped rapidly, and the beginnings of 1-cm 
techniques were well along. 

The problems of getting equipment into pro- 
duction were occupying a larger and larger 
share of laboratory effort, particularly since the 
large radio companies were soon overloaded with 
war work, and the laboratory set about the prob- 
lem of finding and educating new manufac- 
turers. The RL transition office was established 
to assist in these production problems and rap- 
idly grew to be an invaluable part of the labora- 
tory. 

By the end of the year the laboratory had 
reached full maturity. Its component develop- 
ment groups were now well organized, the sys- 
tem groups were at work on a wide variety of 
experimental and production equipments, and 
the engineering and production design activities 
were reaching a firm footing. The Army and 
Navy were looking more and more to MIT-RL 
for assistance in solving tactical problems, as 
well as for help in supervising production de- 
signs. Collaboration with industrial laboratories 
had grown to very large proportions, and the 
standard for future collaboration was set by the 
extraordinary achievement of the Philco Cor- 
poration in bringing a laboratory set to full- 


scale production in nine months by making the 
most extended use of MIT-RL facilities and 
skills. The stream of scientific visitors to and 
from England which began with a trickle in 
1941, continued to swell during the year, result- 
ing in the most intimate exchange of information 
and ideas between this country and the British 
laboratories. 

14 1943-THE RISING TIDE 

Field Applications, The year 1943 might be 
characterized primarily as one of engineering 
and production. The basic ideas already devel- 
oped were sufficient to keep the entire resources 
of the laboratory fully occupied in working them 
into practical form, in working on production 
designs, and now, for the first time, in assisting 
the Army and Navy in problems of training and 
using the large volume of production equipment 
in the field. Every radar component and part, 
hundreds in number, went through engineering 
improvements and expansion in production fa- 
cilities. By June 1943 nearly 6,000 radar sets of 
RL design had been delivered to the Army and 
Navy, 22,000 were on order, and production was 
climbing past the rate of 2,000 sets per month of 
all types. The total dollar value of orders for the 
Services had by that time grown to three quar- 
ters of a billion dollars. Production mounted 
rapidly during the latter half of the year, and 
equipments with trained personnel were reach- 
ing the theaters in large quantities. 

This year also saw the establishment of the 
British Branch of the Radiation Laboratory 
[BBRL], an organization which continued to 
grow in size and effectiveness until the end of 
the European war. Operational success in the 
field had now become commonplace. The naval 
battles in the Pacific were making extensive and 
successful use of the SG and other equipment. 
The campaign against the submarine by both 
Army and Navy Air Forces was in full swing, 
with 10- and 3-cm equipment playing a prominent 
role. Experimental blind-bombing equipment 
was introduced to the Eighth Air Force, and the 
first use of it in Europe occurred in November. 
The SCR-584 accounted for itself brilliantly in 
the Italian campaign and in the Pacific. Im- 
proved models of almost every kind of equip- 


8 


SUMMARY 


ment were being designed to meet the demands 
of field experience or new demands in the 
changing war. 

Personnel Problems. The large number of dif- 
ferent types of equipment, the variety of pro- 
duction and engineering problems, the growth 
of field problems, all put an ever-increasing bur- 
den on MIT-RL personnel. The total number of 
employees rose during the year from 1,700 to 
2,700. A large share of the new acquisitions, 
however, were nontechnical employees, or were 
young and inexperienced. The administrative 
load placed on the senior scientific personnel be- 
came extremely heavy, and more and more re- 
sponsibility devolved on younger staff mem- 
bers. Fortunately a considerable group of young 
but extremely able leaders developed. 

Application of Loran. Ever since the begin- 
ning of the laboratory the Loran work had de- 
veloped and the year 1943 saw Loran introduced 
in wide-scale use in the Atlantic as an important 
navigational aid. Stations were installed with 
MIT-RL help in extremely inaccessible and dif- 
ficult locations in the northwest Atlantic area. 

As the year ended plans for the invasion of 
France were being prepared, and the attention 
of the laboratory turned to the problem of sup- 
plying urgently needed equipment for that the- 
ater. 

15 1944-RADAR IN THE FIELD 

Field Service Bases. The year 1944 saw a large 
share of the laboratory’s effort devoted to direct 
service in the field and to the rapid manufacture 
of experimental equipments for immediate field 
use. BBRL worked intimately with the U. S. 
forces in Europe assisting in the use of new 
equipment and adapting equipment on hand to 
new uses as the needs arose. At home RL re- 
sponded to urgent calls from BBRL for new 
equipment, attachments and modification kits. 
As an example, five laboratory-built MEW sets 
were sent to Europe plus additional indicators, 
beacon kits and many other attachments which 
helped this equipment play an important role in 
that war. 

After D-Day BBRL moved much of its effort 
to the Continent and shortly after the fall of 
Paris set up an advance service base there, to 
remain in closer touch with the field officers. As 


the Battle of France culminated in brilliant and 
rapid success, and the war in Europe appeared 
to be well on its way to completion, the attention 
of MIT-RL swung to the Pacific war, which was 
also reaching its climax. This swing was partly 
checked by the Battle of the Ardennes Bulge 
which required intense consolidation of the ef- 
forts in Europe. Nevertheless, radar in the Pa- 
cific, particularly in the hands of the Navy, com- 
manded increasing attention and met with in- 
creasing success. 

Development of AEW. In early 1944 the U. S. 
Navy proposed to the laboratory the most ambi- 
tious program ever undertaken, the development 
of airborne early -learning [AEW] equipment. 
This extraordinarily difficult job was only a 
dream in March 1944, but its possibilities had 
been proved by the end of the year, and in 
August 1945 a carrier was completely equipped 
with model shop equipment and trained person- 
nel in readiness for the Pacific campaign. 

The year 1944 also proved the versatility of 
microwave equipment. The set designed for anti- 
aircraft fire control became an important link in 
the control of aircraft in tactical air operations. 
The MEW, designed as an early-warning set, 
proved to be a powerful tool in the control of 
both tactical and strategic air forces. Many other 
sets were revised by RL personnel in the field to 
meet new tactical requirements, and the labora- 
tory was called on to produce many attachments 
and modifications for gear already in the field. 

This year saw also the final perfection of 1-cm 
techniques, and orders were placed by both the 
Army and Navy for airborne equipment at this 
wavelength. 

1.6 1945-THE END 

Pacific Activities. Early 1945 saw the war in 
Europe reaching its climax, with BBRL person- 
nel more active than ever in urgent field prob- 
lems there. The war in the Pacific, however, 
seemed destined to go on for two more years. 
Longer term projects for this theater were 
pushed intensely, particularly as Japanese sui- 
cide attacks developed serious proportions. As 
the war in Europe ended, BBRL personnel were 
quickly returned home, and many of them were 
promptly dispatched to the new Pacific branch 
of OSRD which was being set up in Manila. 


WHY MICROWAVES? 


9 


By this time Loran chains had been extended 
throughout the Pacific, throughout the Atlantic, 
over the Continent of Europe, and into the China- 
India Theater. A new type of Loran, operating at 
lower frequency, had shown promising results, 
and an operational chain was being prepared to 
give improved navigational facility over the Jap- 
anese islands. The long-term and extremely large 
effort which had gone into the Mark 56 fire-con- 
trol system for naval ship use reached its cul- 
mination in successful trials, and a large order 
was placed for equipment. The AEW project, 
employing the largest group ever assembled on a 
single project in the laboratory, went through 
its trials, and, as has been mentioned, equip- 
ments produced by the model shop were just 
ready for action as the first atomic bombs were 
dropped and the Pacific war came to its dramatic 
end. 

Termination of Project. At this time, on in- 
structions from OSRD, the laboratory already 
had begun its process of demobilizing the long- 
term research activities and had for some time 
been undertaking no new long-term projects. 
The end of the war brought all activities to a sud- 
den halt, and the process of tearing down in five 
months what had been built up in five years began. 

17 WHY MICROWAVES? 

Advantages of Microivaves. At this point it is 
well to stop and review precisely the factors 
which made microwave radar, as compared 
with longwave radar, so important. There have 
been frequent suggestions of rivalry between 
microwaves and long waves, with implied dis- 
paragement of one or the other. This is unfor- 
tunate, for actually there are applications in 
which each is best fitted for reasons of economy, 
coverage, weight, and other factors. Further- 
more, it is no disparagement of the longwave 
equipments, developed before the days when 
microwave techniques were available, that they 
were in some cases superseded by microwave 
equipment. 

The advantages of microwaves for a large 
number of radar applications depend upon cer- 
tain fundamental physical facts. These facts are 
connected with the two well-known physical 
phenomena of diffraction and interference. 

Diffraction. The phenomenon of diffraction, 


for our purposes, means that when electromag- 
netic radiation passes through an aperture or 
emerges from an antenna or a reflector, the beam 
which results is not as sharp as would be pre- 
dicted from the ordinary laws of geometrical op- 
tics. In fact, some radiation spreads out in all 
directions, but most of it is concentrated within 
a beam the width of which is the greater the 
longer the wavelength and the smaller the aper- 
ture or antenna. Hence, with a given sized an- 
tenna structure, the beam grows steadily nar- 
rower as the wavelength is reduced. Thus, micro- 
wave radar means radar in which the beam is 
relatively sharp. Narrow beams in radar have a 
number of advantages : 

1. The available power is concentrated in a 
smaller region in space, and hence, other things 
being equal, greater range of detection is possi- 
ble with a given amount of power. 

2. Narrow beams give a possibility of higher 
accuracy in determination of the angular bear- 
ing or elevation of a target, an accuracy which is 
important in many applications. 

3. Narrow beams allow higher resolution, 
which means that two targets close together can 
be distinguished as two, rather than giving a 
single, unseparated signal. In other words, a nar- 
row beam gives radar additional “sharpness of 
vision,’' a factor which is of predominant impor- 
tance in such applications as blind bombing. 

4. Narrow beams increase the ratio of the tar- 
get signal to unwanted signals caused by ground 
reflections, sea waves, clouds, or enemy-created 
clutter. 

5. Narrow-beam radar is harder for the en- 
emy to jam by any method, partly because the 
jamming source must be in the narrow beam it- 
self to be effective, and partly because the amount 
of power required for jamming must be com- 
parable to the power concentrated in the beam 
itself. 

Interference. The phenomenon of interfer- 
ence, which also depends fundamentally on wave- 
length, is a factor to be considered in certain 
radar applications. The most important of such 
applications is concerned with the propagation 
of radar beams over the surface of water. In 
this case (unless the beam is so sharp and so 
pointed that none of it strikes the water) the 
phenomenon of interference always appears be- 


10 


SUMMARY 


tween the beam going directly from the radar 
antenna to the target and that which is reflected 
from the surface of the water. Depending on the 
height of the target and, hence, on the difference 
in path traversed by these two beams, the two 
beams will interfere with each other to produce 
either destructive or constructive interference. 
Because of the change of phase of 180 degrees 
which occurs in the reflection itself, this means 
that one always gets destructive interference 
along the surface of the water. 

Indeed, a pattern of maxima and minima is 
set up, the structure of which depends upon the 
height of the antenna above the water and upon 
the wavelength. With low antennas shorter- 
wavelength radiation hugs the water more 
closely, and the pattern of maxima and minima 
is such as to afford less likelihood of a target 
being missed. As a result, radar used on ship- 
board for surface search and detection secures 
great advantage by the use of short wavelengths 
since objects on the surface can be detected very 
much further away. 

Versatility of Application. Finally it should be 
mentioned that since, for a given size of beam, an 
antenna for short waves is smaller than for long 
waves, problems of installation in cramped quar- 
ters on shipboard and in aircraft become easier, 
and it is also more convenient to design special- 
ized antennas for a variety of purposes, antennas 
which give specially shaped beam patterns and 
thus allow a greater versatility in radar appli- 
cations. 

The amount of refraction or bending of radio 
waves by varying water vapor densities in the 
atmosphere also varies with the wavelength. 
There are frequent occasions when very short 
waves are refracted around the curvature of the 
earth to a considerably greater extent than long 
waves. This may be either an advantage or a dis- 
advantage, depending on circumstances, but it is 
a factor to be considered. 

The design of a radar set is a complex prob- 
lem and the factors named above are not always 
of sufficient advantage to overbalance other fac- 
tors which may be present. Nevertheless, each 
of the advantages herewith listed for micro- 
waves has played an important role in enabling 
certain equipments to do things not previously 
possible, or, in many cases, to do them better. 


The advent of microwaves in the radar field can, 
therefore, be regarded as one of the major 
achievements which made radar such a powerful 
tool in World War II. 

18 A SURVEY OF 

MICROWAVE APPLICATIONS 

The complete story of the development and use 
of all the microwave equipment during the war 
is a long one indeed. RL participated in the de- 
velopment of some 100 different types of micro- 
wave equipment which were used in small or 
large quantities, or were nearly ready for use as 
the war ended. These equipments had their effect 
on every aspect of air, land, and sea warfare. 
Even as the war ended it was clear that while 
microwave radar had already profoundly af- 
fected many tactical operations, a still more pro- 
found effect on tactical and strategic plans could 
have been expected if the war had continued a 
year or two longer. Important as were the con- 
tributions of microwave radar, the ultimate pos- 
sibilities have not yet been achieved. A few of 
the highlights of their important use are worth 
brief mention. 

1 In the Air 

The first microwave application was in air- 
borne use and RL has always been largely “air 
minded.” Of the dozens of airborne radar equip- 
ments, there were few successful ones which did 
not operate at microwave frequencies, the U. S. 
Navy ASB, an airborne search set, and the Army- 
RCA Shoran bombing set being the main exam- 
ples. Below are listed some of the major airborne 
applications. 

Aircraft Interception 

The 10-cm AI equipment in the form of the 
SCR-720 became standard equipment for the 
U. S. Army and the RAF nightfighters. This ap- 
plication proved of far more importance to the 
British than to the U. S. Forces, and they put a 
correspondingly large effort on the problem. 
U. S. Navy carrier-based nightfighters were 
equipped with 3-cm AI equipment which had 
many important successes. 


A SURVEY OF MICROWAVE APPLICATIONS 


11 


Surface-Vessel Search 

Equipment of the ASV type for detection and 
destruction of surface vessels and submarines 
played a role of critical importance in the war. 
Many different types of sets were developed for 
this purpose. The first were 10-cm equipments, 
of which the SCR-717 and the Navy ASG were 
the most widely used. Later 3-cm equipment, of 
which the Navy ASD was the first, saw still wider 
use, and 3-cm equipment eventually came to be 
used almost universally by the Navy. 

Equipped with a computing attachment for 
low-altitude bombing, U. S. Army planes with 
SCR-717 equipment accounted for huge quanti- 
ties of enemy shipping in the Pacific area. Ac- 
cording to General Kenney, two squadrons alone 
accounted for nearly one million tons of Japa- 
nese shipping, all destroyed at night and all com- 
pletely by radar detection and attack. The major 
contribution which ASV equipment made to the 
war against the submarine has already been 
mentioned. 

Blind Bombing 

The British were the first to use airborne ra- 
dar for blind bombing of German targets at 
night. The U. S. Air Forces had adopted a policy 
of precision daylight bombing, but it was not 
many months before their experience in cloudy 
Europe convinced them of the necessity for 
equipment for bombing through overcast. A 
large number of planes in both the Eighth and 
Fifteenth Air Forces were eventually equipped 
with the so-called H 2 X equipment, and all of the 
B-29’s had this as standard equipment. 

During the winter months in Europe a pre- 
ponderant part of the bombing was done through 
overcast with radar instruments. During the last 
months of the war high-precision equipment of 
the Eagle type was used by squadrons of B-29’s 
over Japan and turned in spectacular records for 
precision attack. One complete wing of B-29’s 
was especially equipped with Eagle equipment, 
and a second wing was beginning to arrive in the 
theater as the war ended. Blind bombing did not 
approach visual bombing in accuracy, but con- 
tinual improvements were made as training 
problems were better understood, as operational 
planning became more complete, and as comput- 


ing mechanisms were developed. Great improve- 
ments in radar bombing precision could still be 
attained with further development of 1-cm 
equipment and more highly perfected bomb- 
release computers. 

Airborne Fire Control 

Although a large development effort went into 
radar for the control of airborne guns, both the 
German and Japanese Air Forces were destroyed 
without extensive employment of such equip- 
ment. The sets developed ranged from simple 
range-finding sets to complete automatic-track- 
ing equipment for tail turrets. A special range 
finder for use with 75-mm cannon on the B-25 
had considerable use and success. A number of 
B-29’s were equipped with a manually operated 
tracking direction- and range-finding radar for 
the tail turret guns. If future air wars are fought, 
radar gunnery will, no doubt, play an important 
role, for the techniques are well understood now, 
and further development is possible. 

Air Navigation 

Bombing and ASV sets have proved invaluable 
aids to air navigation. It was the navigational as- 
pects which made the sets popular with their 
crews. Navigational equipment for troop-carry- 
ing planes provided by a converted ASV set saw 
service in the European Theater, and orders for 
a more simple light-weight navigation set had 
been placed and production just begun as the 
war ended. 

Beacons 

Radar beacons are a valuable adjunct to air- 
borne radar. Beacon bombing equipment of two 
different types saw operational use. In one, the 
“H” system, beacons on the ground were used in 
conjunction with the airborne microwave radar. 
In the other, a beacon in the aircraft responded 
to radar stations on the ground in the micro- 
wave “Oboe” system. Beacons to mark airfields 
and other important landmarks as navigational 
aids proved of considerable importance. Portable 
beacons carried by paratroopers to mark drop- 
ping zones for oncoming planes also opened up a 
technique of great possibilities and one which 
saw successful operational use. 


12 


SUMMARY 


On the Ground 

The applications of ground-based radar are 
so many and so varied that it is difficult even to 
classify them. A few of the major categories in 
which microwave techniques turned out to be of 
value and in which MIT-RL put considerable 
effort are discussed in the following text. 

Air Defense 

The complete air defense problem involves : 

1. Early warning of approaching airplanes. 

2. Control of intercepting fighters. 

3. Antiaircraft fire control. 

Early Warning of Approaching Airplanes. 
The first and the most widely used early-warning 
equipments which served in large numbers all 
through the war was the SCR-270, developed be- 
fore the war by the U. S. Army Signal Corps. 
Because of the availability and success of these 
equipments, and because of the low-power level 
of early microwave gear, MIT-RL did not under- 
take development of microwave early-warning 
equipment until 1942. By this time high-powered 
microwave magnetrons were available, and ad- 
vantages in the higher resolution of microwave 
equipment were more fully realized. The result 
of nearly two years of intense development ef- 
fort was the so-called MEW equipments previ- 
ously mentioned, which got into commercial pro- 
duction shortly before the end of the war. Lab- 
oratory models of these equipments, however, 
served in Europe and in the Pacific primarily as 
equipments for the control of friendly aircraft 
rather than for the detection of enemy raids. 

Control of Intercepting Fighters. The control 
of intercepting fighters requires radar equip- 
ment of higher precision than that used for early 
warning, and requires, in addition, mechanisms 
for determining the height of friendly and enemy 
planes. Actually the MEW equipment, with an 
auxiliary height finder, proved to be the best 
combination. More compact 10-cm equipment, 
giving height and azimuth on individual planes, 
was developed and put into production as the 
SCR-615 which saw limited use. 

A similar set adapted for shipboard use, how- 
ever, was widely employed. This employed the 
conical-scan principle, also used in the antiair- 
craft gunnery radar discussed in the next para- 


graph. Later height-finding techniques used the 
so-called Beavertail beam which scanned in ele- 
vation giving heights of all planes within a given 
sector simultaneously. Finally the V-beam prin- 
ciple was perfected allowing continuous height 
finding, and scanning. The first models were be- 
ing completed in August 1945. 

Antiaircraft Fire Control. The major effort in 
the laboratory on the antiaircraft fire-control 
radar was the SCR-584 already mentioned. This 
automatic-tracking radar could follow individ- 
ual planes with an accuracy of around one-tenth 
of a degree and a range accuracy of a few yards 
feeding present-position data continuously to a 
suitable computer. This equipment became 
standard equipment for most antiaircraft gun 
batteries, and, in addition, toward the end of the 
war showed many possibilities for adaptation to 
other unanticipated uses. 

Control of Air Operations 

Ground-based radar which gives a wide and 
accurate view of air operations opens up the pos- 
sibility of the control of such operations on a 
large scale. MEW radar, the SCR-584, plus a va- 
riety of special attachments such as computers 
and beacons, etc., give a remarkable facility for 
this purpose. 

As the war ended equipment using the V-beam 
principle was being produced in small quantities, 
and would have given even more complete facili- 
ties for this purpose. The control of both tactical 
and strategic air operations in Europe was car- 
ried on in bad visibility with the 584 and MEW, 
the latter being supplied straight from RL. Air- 
borne beacons were an important auxiliary for 
ground control, extending the range on small 
planes and insuring proper identification. This 
type of technique carries over directly into the 
control of peacetime airway traffic, and the use 
of radar aids in this field shows great possibility. 

Ground Force Operations 

Radar for the use of ground forces in their 
various problems never got into wide use in this 
war because the techniques required were mostly 
beyond the state of the art. Experimental radars 
for the detection of gun and mortar shells, and 
for the detection of moving vehicles and person- 


THE ORGANIZATION OF THE RADIATION LABORATORY 


13 


nel were produced in small quantities and showed 
interesting possibilities. 

Aircraft Landing 

The landing of aircraft in bad visibility on air- 
fields presents a problem in traffic control and 
precision location for which radar aids are 
particularly suitable. The ground control of 
approach [GCA] system is a first and successful 
step toward the solution of this problem. The 
precision and resolution available with micro- 
wave techniques made such a system possible for 
the first time. Some of the production versions of 
this equipment turned in spectacular records for 
saving planes attempting to land under unfavor- 
able conditions. 

At Sea 

With the exception of equipment for long- 
range air warning, practically every radar set on 
modern ships is a microwave set. These sets per- 
form a wide variety of complex functions. 

Fighter Control 

Radar for this function must give precise and 
continuous information on location of friendly 
and enemy aircraft over a wide area. Until re- 
cently, radar techniques were not available to 
meet all the necessary requirements of such 
equipment. A set designed in the laboratory, 
however, known as the SM, has been widely and 
successfully used, together with its lighter- 
weight successor, the SP. Considerable further 
study of the problem and development of tech- 
niques led finally to the design of the SX, which 
was getting into production as the war ended. 
This is the first shipboard set to give full, accu- 
rate data on bearing, distance, and height of all 
planes continuously over a wide area. 

Surface Surveillance and Navigation 

The first application of microwave equipment 
to shipboard use was for the location of surface 
vessels, surfaced submarines and other objects 
on the surface of the water, as well as nearby 
land masses. This opened up tremendous new 
possibilities in the maneuvering of naval forces 
in conditions of low visibility, and large numbers 
of equipment of this type were adapted to every 
kind of naval vessel, and were produced and in- 


stalled on practically every combat vessel of the 
U. S. Navy. Such equipment, with suitable at- 
tachments, was particularly useful in the accu- 
rate navigation required in amphibious landings. 

Fire Control 

The control of naval gunfire requires accurate 
position data to be fed continuously to compu- 
ters. The requirements are particularly severe 
when the targets are aircraft. BTL carried the 
major burden of designing radar fire-control 
equipment for the U. S. Navy throughout the 
war, and as soon as techniques became available, 
BTL engineers made use of microwave fre- 
quencies. 

MIT-RL assisted at various points in this 
work, and in 1943 undertook intensive develop- 
ment of a completely new combined radar and 
computer for the fire control of 5-in. or smaller 
guns for either surface or antiaircraft fire (Gun 
Fire-Control System Mk 56) . Although the final 
laboratory prototypes were not completed until 
November 1945, the Navy has authorized post- 
war production and installation of this equip- 
ment. 

19 THE ORGANIZATION OF 

THE RADIATION LABORATORY 

To understand the way in which the Radiation 
Laboratory was organized and operated it is 
necessary, first, to review the various higher au- 
thorities to which MIT-RL was responsible and 
the channels through which this responsibility 
operated. Ultimately, of course, the director of 
OSRD was responsible for the entire scientific, 
financial, and administrative operation of OSRD 
activities. Actually, after broad policies were 
formulated, the scientific program and its ad- 
ministration was delegated to NDRC, but admin- 
istrative and fiscal matters were handled by the 
contracting officer of OSRD. NDRC, in turn, di- 
vided up the field into some nineteen divisions, 
and made the chief of each division responsible 
for the scientific activities coming within his 
area. Since MIT-RL operated under Division 14, 
the chief of this division. Dr. A. L. Loomis, was 
responsible for setting general policies in regard 
to the scientific program of the laboratory. The 
Division 14 committee served as a sort of board 


14 


SUMMARY 


of directors, passing on general policy matters 
and on matters of budget policy. Thus matters of 
broad general policy came to the director of the 
laboratory from the Division 14 committee. More 
specific instructions came directly from the chief 
of Division 14, and detailed instructions and au- 
thorization on administrative matters were 
handled by the executive secretary of Division 14. 

Contractual matters for which OSRD was re- 
sponsible were handled through a contractual 
arrangement between OSRD and MIT, in which 
MIT was charged with the responsibility of ad- 
ministering and operating the laboratory de- 
voted to work specified by Division 14 of NDRC. 
MIT assumed the responsibility of operating the 
administrative and financial affairs of MIT-RL 
in such a way as to meet the rules and require- 
ments of government contracts. The Division of 
Industrial Cooperation [DIC] served as the 
agent of the MIT administration for managing 
contractual matters, and DIC in turn delegated 
to the director of the laboratory responsibility 
for conducting its administration in line with 
government and MIT policy. 

This mechanism through which OSRD oper- 
ated is reviewed in order to point out that the 
director of MIT-RL was responsible to Division 
14 for the general scientific program of the lab- 
oratory and for general administrative matters, 
and simultaneously was responsible to the presi- 
dent of MIT for matters connected with opera- 
tions on the MIT campus and for matters con- 
nected with contractual obligations. 

When MIT-RL itself was first established, the 
organization was exceedingly simple and infor- 
mal. There were five components of the first ra- 
dar system which needed to be developed, so five 
groups were formed to carry on the work. As 
new problems came up new groups were added. 
Coordinating mechanisms were scarcely re- 
quired at first since the entire group was small 
and, moreover, was an extremely congenial one. 
Eventually the size and diversity of MIT-RL out- 
grew the simple organization, 'and in 1941 the 
division structure was established, which per- 
sisted until the end. Under this organization the 
laboratory was divided into eleven (later twelve) 
major divisions, with a division head in charge 
of each. Three of the divisions had to do with 
business affairs, buildings and maintenance, and 


personnel ; one had to do with advance research ; 
two were devoted to component development; 
and the remaining divisions were devoted to spe- 
cific classes of system problems. Thus one divi- 
sion was devoted to airborne application, one to 
fire control, one to beacons, one to Loran, and 
so on. The director and associate directors, the 
heads of the various divisions, and the associate 
heads, constituted the steering committee of 
MIT-RL which operated as a sort of cabinet. It 
was in this committee that all major problems 
concerning the program of the laboratory were 
discussed. The conclusions reached by the com- 
mittee were put into direct effect by its members, 
who had executive responsibility for the labora- 
tory work. Each division was divided into groups 
devoted to specific problems within the area of 
the division. 

It was the function of the system groups to be 
informed fully in regard to the tactical problems 
in their respective fields. They kept informed on 
these problems, of course, through discussions 
with military and naval officers, with civilians 
returning from the field, and by means of reports 
received from a variety of British and American 
agencies. They were also responsible for being 
generally informed on the technical possibilities 
of radar component design. Thus, as new tactical 
requirements arose, or as new technical develop- 
ments came along, it was possible for the system 
divisions to propose an overall design for a new 
radar equipment to meet a specific tactical need. 
In collaboration with military personnel they 
would write the general characteristics for the 
proposed equipment, and in collaboration with 
technical personnel, write the technical charac- 
teristics. The component groups within MIT-RL 
would then be requested to develop the com- 
ponents required for the new system, and to de- 
liver experimental models to the system group. 
The system group named a project engineer for 
each system who was responsible for coordinat- 
ing the design of the various components; for 
assembling them into a final equipment ; for pro- 
viding for the general mounting and assembly of 
the final equipment, and for its laboratory, field, 
and service tests ; for following through produc- 
tion design ; for assisting in introduction of the 
equipment in the field ; and for working on im- 
provements, attachments, and modifications to 


COLLABORATION WITH MANUFACTURERS 


15 


keep the set adapted to its tactical requirements. 
It was the job of the component groups, on the 
other hand, to take care of all problems con- 
nected with the development, design, engineer- 
ing, and production of the individual component 
parts of the equipment. Thus vacuum tubes of 
various types might need to be developed, engi- 
neered, and put into production. Special circuit 
elements, pulse-forming lines, specially wound 
potentiometers, and dozens of other items might 
have to be designed and put into production by a 
firm which could later serve as subcontractor to 
supply this part for the Army or Navy prime 
contractor. The production design of the trans- 
mitter, the antenna, the receiver, the indicator, 
and other major components was also the respon- 
sibility of a component group, which worked 
intimately with the engineers and the prime con- 
tractor on the final design. As often as not it was 
new developments in the component groups, 
higher-powered tubes, improved circuits, etc., 
which made possible sets for new tactical uses or 
which stimulated major improvements in exist- 
ing equipments. 

The net result was that the design of the new 
radar set was a job which normally involved a 
very large number of individuals in a large num- 
ber of groups throughout MIT-RL. The system 
project engineer had at his command an enor- 
mous supply of highly specialized talent and ex- 
perience in the design and use of almost every 
detailed part of a complete system. Through the 
medium of the component groups, experience ac- 
quired in airborne equipment became available, 
where applicable, to ground and ship equipment, 
and vice versa. The component groups served as 
a large reservoir of research, development, and 
engineering experience, upon which every new 
radar depended, and from which it drew the best 
possible ideas for design. 

The back-and-forth cooperation between the 
system and component groups was one of the 
major factors in MIT-RL operations and in its 
success. 

1.10 COLLABORATION 

WITH MANUFACTURERS 

The story of the intimate collaboration be- 
tween MIT-RL and scores, and eventually hun- 


dreds, of manufacturers, subcontractors, and 
vendors throughout the entire industry is far too 
elaborate and detailed to be related here. It was 
anticipated in the early days that this problem 
would be a relatively simple one. MIT-RL would 
develop a piece of radar equipment, prepare a 
breadboard model for trials, and then, if ac- 
cepted by the Army or Navy, turn this model over 
to a manufacturer, who would take full responsi- 
bility for carrying it from the breadboard stage 
to final use in the field. Such a simple picture 
turned out to be the farthest possible from the 
truth. Rather, one should say that this technique 
was possible only in a very few cases, and these 
were mostly cases where the equipment was 
manufactured by the Western Electric Company. 
In this case the entire facilities of this company 
and BTL, together with their many subcontrac- 
tors, were available to tackle the problem and 
carry it through to completion. Even in this case, 
however, close collaboration between MIT-RL 
and BTL was practiced. 

In general, there were very few companies 
with the facilities and experience required to 
carry through a complex new radar equipment 
from the laboratory stage to full production. It 
was not only that the radar equipment itself was 
new, but scores of parts and components asso- 
ciated with it were also new such as new vacuum 
tubes, new electric circuit components, new die- 
lectrics, new mechanical parts, dozens of types of 
“plumbing” fixtures and parts for the radio-fre- 
quency portion. All these things in general were 
manufactured by subcontractors rather than by 
the prime contractor, and it was the task of the 
research laboratory to see that all these compo- 
nent parts were designed and put into production 
by suitable subcontractors all over the country. 
In addition, test equipment in this field did not 
exist in the early days. Equipment had to be 
manufactured for laboratory development work, 
for factory tests and inspection, as well as for 
test and inspection work in the field. All this 
equipment had to be designed, developed, and 
put into production independently of the produc- 
tion of the radar equipment itself. 

This meant that the research laboratory had to 
have contact with literally hundreds of manufac- 
turers, each of whom was working on the design 
and manufacture of some particular part or com- 


16 


SUMMARY 


ponent of a radar equipment, or of an auxiliary 
equipment associated with radar development 
work and manufacture. A manufacturer of auto- 
mobiles manufactured precision antenna mounts 
for the SCR-584. A producer of locks went into 
production on 3- and 10-cm waveguide elements 
and fittings. Each of these manufacturers had to 
be introduced to the problem, had to train his 
engineers to work out production methods, had 
to be supplied with detailed specifications plus 
necessary test equipment, had to be given initial 
educational orders to get production under way 
in advance of larger Army or Navy orders, had 
to be assisted in the design of special tools, and 
often even had to develop new methods of pack- 
ing and shipping. 

There was no single fixed pattern for handling 
the liaison between the MIT-RL and the manu- 
facturers and vendors. In general, the transition 
office, which was a branch of the office of the 
director of the laboratory (and which worked 
closely with the OSRD transition office), ex- 
plored the industrial field to locate manufac- 
turers throughout the country with special tal- 
ents or experience or facilities for various types 
of manufacturing work. This office maintained 
a list of the plants investigated together with 
current records of their production loads and 
available engineering and manufacturing facili- 
ties. When a new part or piece of equipment re- 
quired manufacturing facilities, the technical 
men consulted the transition office, and with its 
help selected the most promising manufacturer. 
Needless to say. Army or Navy clearance of the 
manufacturer had to be processed if the equip- 
ment had to be classified as secret or confidential. 

Furthermore, the procurement agencies of the 
Army and Navy also had to agree that the 
chosen company would be a suitable one for sub- 
contracting on orders should they later mate- 
rialize. When suitable contractual arrange- 
ments had been made, the company would send 
its technical men to MIT-RL for a period of in- 
doctrination and discussion of the new problem. 
They secured from MIT-RL complete informa- 
tion, drawings, reports, specifications, and other 
data having to do with their manufacturing job, 
and, when necessary, were told how the particu- 
lar component they were to make fitted in with 
others so that they would know what features of 


the design were particularly critical. The com- 
pany engineers would then prepare their own 
drawings for the equipment in question, submit 
them for the approval of the laboratory engi- 
neers until designs approved by all concerned 
were finally worked out. Prototype samples 
would usually be manufactured and tested be- 
fore production lines finally were set up. Where 
necessary the cognizant MIT-RL group main- 
tained a continuous test and check of the produc- 
tion units. In the case of manufacturers chosen 
by the Army or Navy as prime contractors for a 
major piece of radar equipment, the collabora- 
tion became a three-way one between MIT-RL, 
the contractor, and the Army or Navy bureau or 
branch concerned. In this case usually joint co- 
ordinating committees were set up with repre- 
sentatives of the three groups. These held fre- 
quent meetings working out problems of gen- 
eral design, schedules, choice of subcontractors, 
specifications for parts and performance, and 
the scores of other matters that were required 
in order for radar equipment to meet Army or 
Navy specifications and requirements. 

In certain cases a prototype equipment made 
at the laboratory would be transferred to the 
manufacturer’s plant, where the task of whip- 
ping it into a production design would be carried 
out with frequent short and long visits both ways 
between contractor’s representatives and MIT- 
RL representatives. In other cases manufac- 
turer’s representatives would spend weeks, or 
even months, at the laboratory assisting in work- 
ing out the design of the first prototype model in 
order that the job of converting it into produc- 
tion designs would be less involved and so that 
the manufacturer’s own techniques and desires 
could be incorporated right into the early labora- 
tory models. The net result was that at least dur- 
ing the last two years of operation of MIT-RL 
manufacturer’s engineers were generally in on 
the project almost from its initiation until the 
end, and MIT-RL research men followed it 
through the manufacturing design and produc- 
tion process, and finally into the field. 

Ill COLLABORATION 

WITH THE ARMY AND NAVY 

From the day the laboratory was organized 
close collaboration with the Army and Navy was 


COLLABORATION WITH THE BRITISH 


17 


a watchword. The relations were always as in- 
formal as was possible. MIT-RL did not await 
formal requests for undertaking projects, and 
never hesitated to propose new ideas for projects 
to Army and Navy representatives. On the other 
hand, the Army and Navy representatives never 
hesitated to discuss their problems informally 
with MIT-RL, and in this way nearly always 
came to general agreements before formal proj- 
ect requests were passed. 

The Navy was the first to recognize rather for- 
mally the necessity for liaison with the labora- 
tory, and established in 1941 a Navy liaison of- 
fice. Starting with one officer, this office grew 
eventually to have a permanent staff of some 
thirty officers, with temporarily attached project 
engineers running to an additional thirty or 
forty officers. Shortly afterwards the Signal 
Corps established a similar liaison office, and 
later, when the Air Force took responsibility for 
radio and radar development, an Air Force office 
was also set up. These liaison offices were a tre- 
mendous help on both sides. They handled all the 
more formal relations, in addition aided greatly 
in establishing informal contacts and arranging 
for visits. Also members of MIT-RL sat as mem- 
bers of committees of the Joint Communications 
Board of the Joint Chiefs of Staff, and MIT-RL 
frequently organized special civilian committees 
to consider various problems and requested 
Army and Navy membership. A measure of the 
extensive contacts with the Army and Navy is 
the fact that in early 1945 an average of fifty 
officers came to MIT-RL each day for long or 
short visits, discussions, and conferences. This 
did not include the many officers, sometimes run- 
ning to 150, who were here on extended visits for 
training purposes or for rendering assistance on 
particular projects. 

The most important point which MIT-RL 
stressed in its relation with Army and Navy rep- 
resentatives was that the Army and Navy repre- 
sentatives come to MIT-RL not with technical 
problems for the design of an equipment of cer- 
tain size and weight, or with certain power re- 
quirements, but rather that they bring to MIT- 
RL full information on the tactics of operations 
which were of importance and for which radar 
aids might be of use. This gave MIT-RL full 
access to information on the success and fail- 


ure of various tactical methods. After acquiring 
a full understanding of the military problem, it 
would then be the job of the technical people in 
the laboratory to evolve suggestions and ideas 
for the best solution to the problem which they 
could visualize. The laboratory then would come 
up with a proposal for the technical design of 
equipment, accompanied, possibly, by proposals 
for the new tactics which would have to be 
adopted to make best use of such equipment. A 
thorough analysis of tactical and technical prob- 
lems would then ensue until sometimes after 
weeks of consideration and discussion a final 
solution or method of approach would be agreed 
upon. From that time on the technical design of 
the equipment was left largely to the technical 
men in the laboratory, who served, in a sense, as 
the Army’s or Navy’s own technical consultants 
on the problem. 

Usually the relations were not so simple as 
this, but this broad principle became more and 
more to be accepted by all concerned, and many 
of the most spectacular achievements in the ra- 
dar field resulted directly from this type of ap- 
proach. This method of operation emphasized 
the partnership between the civilian scientist 
and the fighting Services, and got away from the 
suggestion that the civilians were working for 
or under the direction of the Army or Navy. This 
established a different relation between the 
Army and Navy and MIT-RL than was possible 
between the Services and their commercial con- 
tractors whose job was to work for the Navy or 
Army to receive remuneration for services ren- 
dered. This is a suitable relationship in the pro- 
curement of equipment. It is hardly a suitable 
one for working out new research problems. 

1 12 COLLABORATION WITH THE BRITISH 

A major feature of the laboratory’s activities 
from the earliest days until the end was the inti- 
mate collaboration with the various British 
agencies involved in design, development, and 
use of radar. This collaboration began with the 
arrival of the British mission, headed by Sir 
Henry Tizard, in September 1940. It was this 
mission which revealed the development of the 
cavity magnetron and which outlined the urgent 
necessity for microwave AI radar equipment. 


18 


SUMMARY 


the laboratory’s first project. As previously in- 
dicated, a member of this mission, Dr. E. G. 
Bowen, remained at the laboratory for some- 
thing over two years. Practically all the early 
concepts of the laboratory as to the techniques 
for using microwaves, as well as their military 
applications, came from Dr. Bowen. Through 
him also the latest information on British devel- 
opments kept coming to the laboratory, and he 
transmitted the latest information from this 
country to the British. Later on. Dr. D. M. Rob- 
inson succeeded Dr. Bowen as British liaison 
representative at the laboratory, and he carried 
on this intimate liaison in an equally effective 
fashion. It would have been difficult to have 
chosen two more able and personable representa- 
tives of British scientists. They won the confi- 
dence of the laboratory personnel and thereby 
exerted a great influence on laboratory work. 

The establishment of the OSRD office in Lon- 
don was a major step toward increasing close 
British liaison on the entire scientific front. Ra- 
dar problems immediately occupied a great deal 
of the attention of this office and continued to do 
so throughout its history. An MIT-RL represen- 
tative was sent as a regular member of this office 
in the early days, and from that time on at least 
one member of that office specialized on radar 
problems. 

Early in 1941 Dr. K. T. Bainbridge was the 
first of many MIT-RL visitors to study at first 
hand the technical and operational problems in 
Britain. As all other scientific visitors after him, 
Bainbridge was greatly impressed with the qual- 
ity of the work going on in England, with the 
generosity with which all information was sup- 
plied by the British scientists and military repre- 
sentatives, and by the urgency of the operational 
needs for improved radar equipment of various 
types. A great stream of MIT-RL visitors went 
to England during 1941-1943, and thereafter 
the British Branch of the Radiation Laboratory 
[BBRL] carried the liaison forward on a still 
larger scale. The existence of the London office 
of OSRD made all this possible. It furnished a 
headquarters in England for MIT-RL represen- 
tatives, and members of the office were invalu- 
able in guiding representatives to proper agen- 
cies, laboratories, and personalities in the Brit- 
ish radar picture. Great credit goes to the two 


men who served in succession as head of the 
London mission, Frederick L. Hovde and Ben- 
nett Archambault. Through their efforts and the 
efforts of their staff all significant British re- 
ports in the radar field were quickly collected 
and forwarded to this country, where they were 
eagerly read by RL members. Especially urgent 
items were transmitted by cable, and later by 
teletype. 

In the meantime many British visitors came 
to this country with latest information, samples 
of equipment, and reports on recent develop- 
ments. 

Through these visitors in both directions, 
through the transmission in both directions of 
reports, and through the exchange of informa- 
tion by cable it can be said that both British and 
American scientists were always fully in touch 
with each other’s work and that new ideas aris- 
ing on either side were quickly incorporated into 
the development work on the other side. There is 
hardly a feature of modern microwave equip- 
ment which does not contain a multitude of both 
British and American ideas, and, indeed, hardly 
an idea arose on either side which could not 
trace some of its aspects back to suggestions re- 
ceived from across the Atlantic. 

The main scientific liaison between the two 
countries in the radar field was between MIT-RL 
and the Telecommunications Research Estab- 
lishment [TRE] , a laboratory set up by the Min- 
istry of Aircraft Production. This laboratory, 
like MIT-RL, drew its staff largely from uni- 
versity physics research laboratories through- 
out England. Hence the point of view and method 
of approval of TRE and MIT-RL were always 
nearly the same, and a quick and intimate under- 
standing between the two groups always existed. 

Two other large laboratories, however, were 
also involved. These were Air Defense Research 
and Development Establishment [ADRDE], lo- 
cated also at Great Malvern, and the Admiralty 
Signal Establishment. The former was operated 
under the Ministry of Supply and was devoted 
to Army problems, while the latter, of course, 
dealt with problems of naval radar. Since MIT- 
RL worked in these fields also, intimate contact 
with these two laboratories was kept up. It was 
largely because these organizations were smaller 
and were less involved in fundamental micro- 


^SECRET 


FIELD SERVICE 


19 


wave development than TRE that the relations 
with TRE were more extensive. 

Partly because the relations between the civil- 
ian research establishments and the correspond- 
ing Armed Services were so intimate, RL con- 
tacts with the British Army and Navy and the 
RAF were also very close. British officers were 
always extremely helpful, frank, and intelligent 
in discussing the applications of radar to military 
problems. Discussions with them, visits to their 
radar stations, to operational airfield, and head- 
quarter agencies, contributed very greatly to the 
understanding by RL members of operational 
and military problems met with in the field. MIT- 
RL owes a debt of gratitude to many British offi- 
cers at all levels with whom its personnel estab- 
lished the closest working relations. Many of 
these officers visited MIT-RL at Cambridge, 
Massachusetts, during their visits to the United 
States, and further cemented ties of mutual un- 
derstanding and friendship. 

Liaison with radar experts in the other British 
dominions, while on a smaller scale, was equally 
friendly. There was continual interchange of in- 
formation with the National Research Council at 
Ottawa and its various members, a number of 
whom spent considerable time in RL in the early 
days. Liaison officers from Australian and New 
Zealand agencies also kept in close touch with 
the work at MIT-RL through frequent visits. 

To sum up, the liaison with British agencies in 
the radar field was a major feature of MIT-RL 
work, and, indeed, a major feature of the entire 
radar enterprise of the Allied nations. Not only 
in MIT-RL, but also in the various branches of 
the U. S. Armed Forces and in the great Amer- 
ican industrial laboratories, British-American 
collaboration was continually emphasized and 
was always effective. 

1 13 FIELD SERVICE 

Possibly the most unique and far-reaching as- 
pect of the activities of RL was its field service, 
defined as work directly with U. S. Army or U. S. 
Navy agencies at locations outside of the imme- 
diate vicinity of Cambridge, Massachusetts. It 
could be divided into domestic field service and 
foreign field service. 

Domestic field service included the very large 


amount of work done at U. S. Army and U. S. 
Navy bases, proving grounds, training centers, 
and other stations in the United States. At these 
bases the possible tactical uses of radar equip- 
ment were first explored, operating procedures 
for employment were worked out, problems of 
installation and maintenance were met, and the 
training of operators and maintenance personnel 
went forward. The work of MIT-RL personnel 
at these bases, though not spectacular, had an 
important bearing on the effective introduction 
of radar equipment into combat. 

The field service outside of the United States 
constituted an extraordinary activity. It began 
in late 1942 with a small expedition to the Pan- 
amia Canal Zone which took along special equip- 
ment to improve the air defense coverage of that 
vital area. It ended on V-J Day with a large 
group of MIT-RL personnel scattered through- 
out the Pacific, working intensely on the radar 
problems connected with the plans for the final 
assault on Japan. During the intervening three 
years hundreds of MIT-RL members journeyed 
to practically every theater of operation and to 
many remote bases to assist in introduction, in- 
stallation, modification, and use of new radar 
equipment. 

Although the greatest organized effort was 
represented by BBRL, extremely effective and, 
in many ways, more exciting work was accom- 
plished by individuals or small teams who jour- 
neyed to remote locations on special missions. 
The adventures of the laboratory representative 
who supervised the installation and initial oper- 
ation of the first Loran stations along the wild 
coast of Newfoundland and Greenland make an 
unequaled adventure story. The account of the 
representative who roamed the Pacific, visiting 
every base where the SCR-584 was in use, who 
followed a 584 ashore on Luzon a few hours after 
the first troops went in, and whose efforts put the 
584 on the map as an operating instrument 
throughout the Pacific area, is another tale of 
high adventure and accomplishment. Others 
went into India and China to introduce Loran 
and radar equipment which greatly assisted in 
reducing huge losses suffered in operating over 
the “Hump.’^ 

In the summer of 1943, discussions between 
the British and American representatives on the 


20 


SUMMARY 


occasion of the Compton Radar Mission to Eng- 
land resulted in the proposal that MIT-RL rep- 
resentatives be sent to England to collaborate 
with the British in developing an improved type 
of navigational bombing equipment which the 
RAF needed and which the growing U. S. Air 
Forces would probably need. This was the begin- 
ning of the British Branch of the Radiation Lab- 
oratory, which occupied quarters supplied by the 
Telecommunications Research Establishment 
located in Great Malvern, Worcestershire. This 
initial cooperative effort resulted in the develop- 
ment of the so-called microwave “Oboe” system, 
which was widely used by the RAF and the U. S. 
Ninth Air Force. In the fall of 1943 the first 
radar bombing equipments for the use of the 
Eighth Air Force were sent to England, accom- 
panied by MIT-RL experts, who were also at- 
tached to the British Branch. From that time on 
the projects undertaken by the BBRL rapidly 
multiplied. Many of them had to do with collab- 
oration with the British, but as time went on the 
major problems were those concerned with as- 
sisting the U. S. Air Forces. 

By the spring of 1944 BBRL had grown to 
such a size and its. activities had become so wide- 
spread that it was felt desirable to establish a 
more intimate tie between it and the U. S. Army 
Air Forces. In collaboration with the expert con- 
sultant to the Secretary of War, Dr. E. L. Bowles, 
a civilian staff section, known as the advisory 
specialist group, was organized under General 
Spaatz, Commanding General of the U. S. Stra- 
tegic Air Forces in Europe [USSTAF]. A mem- 
ber of MIT-RL was appointed a member of this 
staff, which served as an official liaison between 
the Air Forces and the civilian laboratories. The 
British Branch of the Radio Research Labora- 
tory, known as ABL-15, was set up in a similar 
way. 

This arrangement enormously improved the 
effectiveness of collaboration between the U. S. 
Forces and the civilian scientists since it gave the 
scientists a quasi-official status in the various 
Army commands. 

BBRL took an intimate and effective part in 
assisting in planning, and in providing radar 
equipment for the invasion of France. Equip- 
ment on hand was modified, new parts and at- 
tachments for existing equipment and whole new 


equipments were sent quickly from the U. S. in 
order to provide the invading forces with the 
best possible radar equipment. BBRL experts 
followed the equipment into France, and after 
the fall of Paris, they set up an advanced service 
base in that city. The laboratory at Great Mal- 
vern still served as the main headquarters, and 
the development and test of new equipment and 
attachments was carried on there. The advanced 
service base, however, served as the headquar- 
ters for those operating with advanced air bases. 
With the assistance of BBRL personnel radar 
aids for tactical air operations were developed 
by the Ninth Air Force and its various tactical 
air commands in such a way that entire new op- 
erational procedures for carrying on tactical air 
operations, particularly at night and in bad 
weather, were evolved. Ninth Air Force Com- 
manders have stated that the effectiveness of 
their units was doubled by the help of civilian ex- 
perts, who worked with them on radar and tac- 
tical problems. 

The enormous problem of introducing blind 
bombing into strategic air operations in the 
Eighth Air Force required continual assistance 
and attention from BBRL experts. The initial 
equipments, as always, were adequate for the 
solution of the problem, and improvements, mod- 
ifications, and the introduction of new tech- 
niques went forward week by week. As large 
numbers of production bombing equipments ar- 
rived, many maintenance and repair bases had to 
be established, test and maintenance procedures 
set up, test and training equipment designed 
and put into operation. A group from BBRL was 
sent to Italy to assist the Fifteenth Air Force in 
similar problems, as well as to work with the 
Tactical Air Forces in the Italian Theater. 

The efforts of civilian scientists, working 
closely with field commanders, were enormously 
appreciated by all the units with which they 
worked. All felt that having close at hand the 
advice of technical experts was invaluable in in- 
troducing new equipments. New equipment af- 
fects tactics, and changes of tactics affect the 
requirements of the equipment. Only through 
intimate back-and-forth discussions on the spot 
could the changing requirements of war be 
kept up with and could new equipment be 
adapted to the problem at hand. Even standard 


FIELD SERVICE 


21 


equipments in large production and use were 
frequently adapted to new uses or modified to 
meet new tactical situations. The experience of 
BBRL and of other similar scientific groups in 
the war theaters has, it is believed, proved con- 
clusively that in a technical war civilian scien- 
tists must play an important role not only in the 
laboratory but at the battlefront. 

In May 1944, following a visit of Dr. K. T. 
Compton to the Pacific Theater, two units were 
set up in that area. The first was a small research 
group to collaborate with scientists of the Radio- 
physics Laboratory at Sydney, Australia, on 
problems of importance to Australian and U. S. 
forces in that area. This group helped introduce 
the latest microwave techniques to the Austra- 
lian laboratory and assisted in the design of new 
equipment required in that theater. As the front 
moved away from Australia, this group became 
isolated, however, and was withdrawn. A second 
group was set up under OSRD auspices in Pearl 
Harbor, to operate with the Army Command in 
that area. This group assisted in radar matters 
with units of the Army which were staged in the 
Pearl Harbor area for forward operations. It 
also collaborated with the Navy in introducing 
new radar techniques, particularly for amphib- 
ious operations. 

In early 1945 a Pacific Branch [PB] of OSRD 
was established in Manila, with a large radar 
section. An advisory specialist group, set up in 
the headquarters of the Far Eastern Air Force, 
served to tie the radar team into the Air Force 
Command. The radar group of PB-OSRD en- 
gaged at once in assisting with plans for the 
invasion of Japan. Extensive work in introduc- 
ing radar aids for this operation and in training 
for the use of them was well under way when 
the end of the war suddenly came. A small and 
less formally organized group was attached to 
the Twentieth Air Force. 

It is of greatest importance to recognize that 
the effectiveness of all the field service groups 
depended not only on the ability, skill, and 
adaptability of the men who went to the field, but 
to an even greater extent upon the support which 
the field group received from the home labora- 
tory. The group in the field was only a forward 
branch of a strong, active development group at 
home. Problems are solved in the field only partly 


by making suggestions or revising equipment on 
the spot. To a much greater extent they are 
solved by the introduction of new pieces of equip- 
ment, either attachments or modifications of 
equipment in the field, or completely new equip- 
ments supplied quickly from the home base. In 
this way the field group could not only propose 
solutions to problems, but could provide within a 
short time the necessary equipment to accom- 
plish the solution. It is estimated that for each 
man in the field from three to five men at the 
home laboratory were occupied on the average in 
designing, building, and shipping equipments 
called for from the field, in supplying informa- 
tion, and in working with Service agencies and 
manufacturers in the United States, in modify- 
ing production equipment, altering training 
procedures or equipment, and many other things. 

Actually, of course, one did not set aside a 
specific three or four hundred men at the home 
laboratory to support the work of one hundred 
men in the field. Rather, the one hundred men in 
the field could call upon the talents and abilities 
of any one or a number of three thousand men 
and women at the home laboratory. These three 
thousand supplied a host of special techniques 
and skills and expert knowledge in all possible 
fields. Hence the group in the forward area could 
be sure that each of their problems could be 
handled by some specialized group at the labora- 
tory. Furthermore, for rush jobs a very large 
'Task force” could be assembled at the labora- 
tory and thrown into the job of rushing snecially 
built equipment to the forward area. Actually, 
therefore, each man at the front had behind him 
thirty men at home, not all of whom he used all 
the time, but upon any one or more of whom he 
could call for specialized help. In short, the field 
laboratory group was only as strong, but was 
fully as strong, as the group at home. 

The imnact of the field service groups was felt 
not only directly at the battlefront, but in every 
aspect of the activities in the zone of the interior. 
New experiences in the field were translated 
quickly into the design of new eouipment, into 
alterations in factory production lines, and even 
in Army and Navy training and procurement 
policy. Often the fastest, the most comnlete and 
most useful information concerning field condi- 
tions as it affected radar equipment came via the 


22 


SUMMARY 


civilian channels. The weekly teletype confer- 
ences with the field groups were read as avidly 
in the Pentagon Building as in MIT-RL. 

For these reasons, an important aspect of the 
effectiveness of a field service group was the ade- 
quacy of its communications with the home base. 
The main tie-line between all of the major field 
units in Europe and the Pacific and the home lab- 
oratory was a weekly teletype conference. This 
conference would last from one to three hours, 
and during it a large amount of information 
could be passed both ways, problems could be 
discussed back and forth on the spot, and solu- 
tions agreed upon. Supplementing the teletype, 
adequate and fast cable service was also essen- 
tial for quick day-by-day messages ; and finally 
it was essential not only to have channels for the 
communication of information, but for the 
transportation on rapid schedules, with high 
priority, of personnel and equipment. In some 
cases it was possible to have equipment arrive in 
the field within less than a week of the time it 
had been requested by cable or teletype. 

Obviously this rapid communication and 
shipment system was clearly ‘'out of channels” 
as far as the Army was concerned. Yet its vast 
usefulness was recognized by the Army itself, 
which provided most of the facilities em- 
ployed. Many of the activities by the civilians in 
the field were equally out of channels from the 
Army point of view. The value of this too was 
recognized, and, indeed, the civilian method of 
operation was encouraged. On technical matters 
the formal channel, through Service Command, 
is often not suitable, important though such for- 
mal channels undoubtedly are in operational 
matters. The civilians, of course, had to learn to 
coordinate their efforts through various cogni- 
zant Army agencies and officers, and where this 
was not done confusion sometimes resulted. But 
this was a small price to pay for the fast-acting, 
effective assistance which civilian field groups 
were able to render. 

1.14 PERSONNEL 

An organization of any type, and especially a 
research and development organization, is no 
stronger than the men and women of whom it is 


composed. In this respect MIT-RL was exceed- 
ingly fortunate. In the early days of 1940 and 
1941 it was able to attract to its ranks some of 
the outstanding and most active young physi- 
cists and engineers in the country. The accom- 
plishments of MIT-RL are a tribute to the intel- 
ligence, the skill, the energy, and the enthusiasm 
of this great group of men. Probably never be- 
fore in history had such a large, able group of 
physicists been assembled on a single project. 
This record was probably surpassed by the Los 
Alamos Laboratory of the Manhattan District 
engineers, but a number of the key individuals 
in that laboratory were acquired by transfer 
from the original MIT-RL group. The problem 
of microwave radar was undoubtedly ripe for 
the picking, but only a keen, active, and enthusi- 
astic group could have plucked its fruits so 
effectively. 

The keenest group of minds working individ- 
ually, however, could never have accomplished 
what MIT-RL accomplished. Equally important 
was the congenial spirit of cooperation which 
permeated the entire laboratory from its first 
day until its last. Large as the laboratory eventu- 
ally became, it always acted as one great family. 
The problems of one part or one group were the 
problems of all. Each individual member was 
willing and eager to do the tasks assigned and to 
work with whatever other individuals could be 
of help. No one can analyze how this spirit grew 
up and was maintained. It came not as the result 
of a conscious effort, but by a mutual desire 
which seemed to be conveyed quickly to each new 
recruit. But there are many things which con- 
tributed to keeping this spirit alive. The follow- 
ing are a few of these things. 

1. The laboratory had only one purpose — to 
help win the war. It was organized at a time of 
impending danger and had its rapid growth dur- 
ing a time of great national peril. A deep, but 
usually unexpressed, patriotic motive actuated 
each individual. 

2. The scientific and military problems on 
which MIT-RL worked were challenging and 
fascinating ones and all MIT-RL members felt 
they were making a real contribution to the war. 

3. The laboratory was a temporary organiza- 
tion. It had no future career; its individuals 


PERSONNEL 


23 


could have no long-term personal ambitions. Its 
job was to do its part in time of crisis and then to 
disband. It was organized from nothing, and 
therefore inherited no dead wood, no precon- 
ceived ideas, no red tape, no rigid organization. 
It was building for the present and not for the 
far future, and flexibility and rapid accomplish- 
ment were its main objectives. 

4. Fixed and rigid procedures were avoided 
as far as possible, although some became inevita- 
ble as the organization grew large. In all cases, 
however, individuals felt that they could accom- 
plish their task quickly and effectively with a 
minimum of interference and red tape. Great 
freedom was left to the individual, but great re- 
sponsibility was placed upon him. All but a small 
minority met this challenge. Each division head, 
group leader, section head, or project engineer 
was given full responsibility for his task, accom- 
panied by full authority to take whatever steps 
were necessary to accomplish it. Effectiveness 
was the goal, rather than efficiency, but in a 
larger sense, a greater efficiency was thereby 
achieved. 

5. Salary scales were fairly and impartially 
determined. No specific salary was ever attached 
to any specific position or responsibility in the 
laboratory. Hence a change of responsibility or 
authority could be quickly made without raising 
complex questions of salary adjustments. Rather, 
salaries and wages were determined on the basis 
of experience of the individual, of his overall 
value to the laboratory as judged by those most 
closely associated with him, and, in the case of 
those who came on leave from permanent posi- 
tions, by the salary received at the previous posi- 
tion. Positions of greater responsibility were as- 
pired to by members of the laboratory only 
because this was a recognition of their ability and 
value and not because they carried a larger sal- 
ary. The financial problem was thus removed 
from consideration in assigning tasks and re- 
sponsibilities or in changing assignments as the 
program of the laboratory required or as the 
achievements and abilities of the individuals 
suggested. 

6. A strong, active personnel organization, 
with the welfare of the individuals in the labora- 
tory its only objective, supervised and adminis- 


tered all matters of personnel policy. A thousand- 
and-one minor matters, involving not only sal- 
aries but traveling and moving expenses and 
working conditions within the laboratory, were 
taken care of by Dr. F. W. Loomis, as associate 
director of personnel, with a foresight, ability, 
imagination, and keen interest in the welfare of 
each individual which won for him and for his 
organization the respect and admiration of the 
entire laboratory. No other factor contributed as 
much to the spirit and enthusiasm of the labo- 
ratory as this effective administration of per- 
sonnel matters. To each and every employee 
MIT-RL was “a fine place to work.” 

Finally, and above all, it should be emphasized 
that MIT-RL was fortunate in acquiring a fine 
group of leaders. It was particularly fortunate 
in the men who headed its major groups and di- 
visions. Many of these groups and divisions were 
very large organizations by themselves. The 
problem of operating them was difficult and the 
responsibility heavy. On the one hand leaders 
seemed to develop, as the need for them arose ; 
on the other hand the organization of the divi- 
sions and groups was built around the key indi- 
viduals who were available. MIT-RL never ad- 
hered to a rigid organization chart based on so- 
called logic or preconceived function; rather, 
the organization was built around the individ- 
uals available. The number of divisions, for ex- 
ample, was determined as much by the number 
of men of division head caliber as by the number 
of logical compartments into which the work 
could have been divided. If any particularly ob- 
vious ‘"principle of organization”'^was adopted by 
the laboratory, this was it. A new section, a new 
group, a new project, a new division was created 
only when there was an obvious leader to head it. 
Frequently when key individuals were called 
away from the laboratory, or were transferred 
to other activities, the group or division they left, 
if there was no obvious successor, was reorgan- 
ized to fit the capacities and abilities of those 
leaders who remained behind. Whether or not 
such a policy is suitable for other types of or- 
ganization, for one devoted to research and de- 
velopment where the insight and imagination of 
individuals is the entire basis of success, this 
organizational policy seems to work. 


24 


SUMMARY 


115 CONCLUSION 

This story (it is not a report) of MIT-RL 
covers only a few of the highlights of the work 
and achievements of a great organization. Apolo- 
gies are due to the many men whose efforts and 


success made the laboratory what it was but who 
are not specifically mentioned in this paper. 
Every member of the steering committee, every 
group leader, every staff member and employee 
shares the credit for what was done. It is unfor- 
tunate that this story so inadequately covers the 
tremendous work accomplished. 


Chapter 2 

THE ORIGIN OF MICROWAVE RADAR AND LORAN NAVIGATION 
DEVELOPMENTS IN THE NDRC 


2.1 INTRODUCTION 

O NE OF THE LARGEST and most active divisions 
of the National Defense Research Commit- 
tee [NDRC] , Division 14, has been almost wholly 
concerned with developing improved radar 
equipment for the Armed Services in cooperation 
with American industry, the development lab- 
oratories of the Army and Navy, and our British 
allies. Although the scientists of NDRC entered 
the field only a year before Pearl Harbor, they 
have participated in the development of very 
nearly half the $3,000,000,000 worth of radar 
and associated equipment delivered to the Armed 
Services by July 1945. Their activity ranged from 
fundamental research on the behavior of super- 
high-frequency waves (microwaves), through 
the development of new vacuum tubes, new cir- 
cuits, and new radar components, to the design 
of complete radar systems serving widely differ- 
ing military purposes. In cases where a small 
number of units were urgently required by the 
Services these have been manufactured with the 
utmost speed by NDRC facilities. Finally, the 
work of the division has included, in many in- 
stances, an important share in the introduction 
of this new equipment into operational use in the 
field. 

Distribution of Development Projects 

The radar research and development of Divi- 
sion 14 was mainly concentrated in a single large 
secret laboratory, the Radiation Laboratory 
[RL], created by virtue of a contract with the 
Massachusetts Institute of Technology [MIT]. 
A number of smaller contracts were placed with 
other educational institutions, chief among them 
being Columbia University, and with industrial 
concerns supplementing the work of MIT-RL 
in a wide variety of component research and sys- 
tems development and engineering activities. 
During World War II the number of NDRC con- 
tracts has averaged about 50.^ The manufactur- 

aSee complete list of OSRD contracts for Division 14, 
NDRC at back of volume. 


ing facilities of industry were relied upon for all 
full-scale production under Army and Navy con- 
tract; but Division 14 had its own model shop, 
the Research Construction Company, Inc. [RCC] 
in Cambridge, Massachusetts, which worked in 
close cooperation with MIT-RL and shared with 
it the burden of manufacture under crash pro- 
grams. By the end of August 1945, approxi- 
mately $25,000,000 worth of radar equipment 
had been directly supplied to the Services by RCC 
and MIT-RL, slightly less than half of which had 
been produced by RCC. 

Scope of Research and Development 

Approximately 150 distinct radar systems 
were developed as a result of this research pro- 
gram, for use on land, at sea, and in the air, and 
for purposes ranging from early warning 
against enemy aircraft to blind bombing and an- 
tiaircraft fire control. The only section of MIT- 
RL not devoted to radar was responsible for the 
development of Loran, a pulsed long-range navi- 
gational aid widely used by the Armed Forces of 
America and Great Britain. A total of $71,000,- 
000 worth of Loran equipment, all but one item 
of which had been developed in whole or in part 
by MIT-RL, was purchased by the Army and 
Navy by the end of July 1945. 

The field activities of MIT-RL personnel took 
them to all principal theaters of war, to the 
European and Mediterranean fighting fronts, 
the China-Burma-India Theater and the South 
Pacific. A British Branch of the Radiation Lab- 
oratory [BBRL], a small group in Australia, one 
at the Mediterranean Allied Air Forces head- 
quarters at Caserta, and an advanced service 
base in Paris backed up the efforts of the field 
representatives and drew in turn upon the re- 
sources of MIT-RL. When the war ended, some 
twenty-five MIT-RL men were in the Pacific or 
en route, while many others were standing by to 
man the radar laboratory it was planned to es- 
tablish in Manila. 

At the end of the war, nearly 5,000 persons 


25 


26 


RADAR AND LORAN NAVIGATION DEVELOPMENTS 


were engaged in radar development under Divi- 
sion 14 contracts, and of these over 3,900 were 
employees of MIT-RL. The nucleus of nearly a 
thousand scientists at this laboratory was drawn 
from universities and colleges in all parts of the 
country. 

During the year 1944-45 the NDRC was allo- 
cating over $4,000,000 each month to Division 14 
and the division received total allocations of 
$141,000,000 for the development of radar and 
Loran equipment since November 1940. When 
the amount spent on research and development 
is weighed against the dollar value of equipment 
actually delivered by July 1945, the sums in- 
vested seem relatively modest. Every dollar 
spent for research and development has pro- 
duced a little over ten dollars worth of military 
equipment. 

This statistical picture can convey some notion 
of the vastness of the enterprise, but it can give 
only an imperfect idea of its military contribu- 
tions. The importance of the NDRC program to 
the allied war effort lies as much in the character 
of the new developments as in their magnitude. 
It is the successful development of radar using 
microwaves (i.e., radio waves only 10 cm in length 
or shorter) that distinguishes most sharply the 
NDRC development program from that of the 
Army and Navy laboratories. Although devel- 
oped and perfected after 1940, microwave radar 
has seen extensive operational use and is largely 
responsible for making modern radar equipment 
as versatile and flexible a weapon as it became in 
the course of World War II. 

The reasons underlying the importance of the 
development of radar systems employing micro- 
waves has been discussed in Section 1.7. There it 
was pointed out that while range accuracy is not 
affected, the narrow beam made possible by such 
wavelengths greatly improves the accuracy of 
bearing location, the effective power, and the 
low coverage of the set and further makes more 
difficult the jamming of the set by enemy action. 

2.2 RADAR BEFORE 1940 

The early history of allied radar development 
has been briefly sketched in the release of the 
Joint Board on Scientific Information Policy 
and the nearly simultaneous release by the Brit- 
ish Information Services. The story need not be 


repeated here. It is only proposed in this section 
to give a summary account of the state of radar 
development in the United States and England 
at the time of NDRC's entry into the field in the 
summer of 1940. 

Viewed in retrospect, with the advantages of 
hindsight, the amount of engineering effort put 
on the radar program in the United States before 
the war seems woefully small for a nation of this 
size. Although work on pulse radar had been be- 
gun somewhat over five years before, it is doubt- 
ful if as many as two dozen persons were en- 
gaged full time on pulse radar research at the 
time of the outbreak of the European war in 
September 1939. 

Early British Developments 

The British had moved much faster, partly be- 
cause of their greater proximitj^ to the threaten- 
ing danger. Under the encouraging wing of a 
highly placed advisory committee capable of as- 
suring ample funds, radar research went for- 
ward rapidly betvs'een 1935 and 1940 in Admi- 
ralty and Army laboratories, and with marked 
success. The work originated in a specially cre- 
ated Air Ministry laboratory staffed hy civilian 
physicists and engineers freshly recruited from 
the universities and industrial concerns. In Sep- 
tember 1939 this laboratory numbered 200 to 300 
persons. 

Early U. S. Developments 

Six months after the outbreak of war in 
Europe, when the Wehrmacht startled the world 
by crashing through the Low Countries, the 
American radar effort still was barely under 
way. In May 1940, the Navj’ received its first 
production unit of the historic CXAM, the earli- 
est radar designed by the Naval Research Lab- 
oratory [NRL]. No production contracts for 
Army radar were let until August 1940. Although 
the Signal Corps laboratories had designed two 
excellent radar systems, prototvT)€s of the SCR- 
268 and the SCR-270, production versions of 
these systems did not appear until early in 1941. 
Neither the Army nor the Navy had seriously 
undertaken the development of an airborne ra- 
dar system. 

The Navj^’s CXAM, the now obsolete patri- 
arch of American radar systems, was an aircraft 
warning set for larger naval vessels. The Army’s 


RADAR BEFORE 1940 


27 


first search sets, the SCR-270 and its successor 
the SCR-271, were land installations designed to 
give long-range detection and early warning 
against aircraft. The SCR-270 was a mobile in- 
stallation transported by four trucks and a 
trailer, while the SCR-271 was a permanent in- 
stallation with an operating building and the an- 
tenna on top of a fixed tower. The SCR-268 was a 
mobile set designed for searchlight and anti- 
aircraft fire control. 

From the present-day point of view these sys- 
tems represent an early stage of the art. The de- 
fects that are mentioned at this point are inher- 
ent in the wavelengths that were the only 
practical choices at the time the sets were de- 
signed. It should not be forgotten that these sets 
were the only ones with which the Armed Serv- 
ices were provided at the time of Pearl Harbor. 
They continued to perform notable services to 
the last day of the war, often in conjunction with 
microwave equipment and often (such are the 
vagaries of procurement and logistics) in areas 
where microwave equipment had not penetrated. 

All these early sets operated at frequencies of 
200 me per sec or below (wavelengths of IV 2 rn 
or longer) and were provided with stacked array 
antenna systems giving at best about a 10-degree 
beam. The accuracy of bearing determination of 
the search systems was only about 3 or 4 degrees, 
but the sets gave excellent range. They gave no 
low coverage, provided poor target discrimina- 
tion, and proved easy to jam. The CXAM had no 
height-finding features and the SCR-270 and 271 
could only estimate the height of approaching 
aircraft by making use of the known pattern of 
the multiple-lobe beam produced by the ground 
reflections. This required careful calibration of 
the pattern at the chosen site and gave only 
approximate results. 

Since the SCR-268 was designed as a precision 
pointing set, its maximum range is only 25 miles. 
It is beset by siting problems and difficulties 
from ground reflections, and during the war its 
utility was seriously impaired by enemy jam- 
ming. A higher degree of accuracy than was in- 
herent in its 10-degree beam was attained in the 
measurement of azimuth and elevation by means 
of a technique called lobe switching using a di- 
vided beam. A positioning accuracy of about 1 
degree was possible by this method. 


Problems of Designs in Field Use 

By June 1940, the British had made great 
strides. The center of radar activity was the Air 
Ministry Research Establishment [AMRE] 
which had just moved to a site near Swanage on 
the south coast of England, and had grown to be 
a large affair. The development of radar systems 
was also going forward at the Army’s Air De- 
fense Research and Development Establishment 
[ADRDE] at Christchurch, at the Admiralty 
Signals Establishment at Portsmouth [ASE], 
and at the Royal Aircraft Establishment [RAE] 
at Farnborough. 

Besides the east coast chain of early-warning 
[CH] stations, which were already in service but 
had not yet been seriously called upon in the de- 
fense of Britain, the British had several other 
systems in use and still more in development or 
production. A small number of mobile units had 
been sent to France with the British Expedition- 
ary Force in the fall of 1939. The British ground 
systems, all of which operated on frequencies be- 
low 200 me, had the same defects enumerated in 
the case of American equipment. 

Of major importance, because this experience 
became the basis of the work of NDRC, were the 
pioneer efforts of the British in the field of air- 
borne radar. This was of two main types : air- 
craft interception [AI], equipment for night- 
fighting aircraft; and air craft-to-sur face-vessel 
[ASV] equipment for the detection from the 
air of ships and surfaced submarines. Primitive 
versions, hardly better than experimental, of 
both types of equipment were introduced into 
Service use somewhat prematurely during the 
fall and winter of 1939-40. No operational suc- 
cesses are unequivocally on record for either type 
of set. Improved versions of both types, thor- 
oughly engineered and well designed, were just 
reaching completion in June 1940 and were in- 
troduced into operational use in the autumn of 
1940. 

These two historic pieces of equipment, known 
as ASV Mark II and AI Mark IV, both appeared 
in time to exert a telling effect upon the enemy. 
The ASV Mark II was used with great success by 
the Coastal Command of the RAF in the North 
Sea, the Channel, and the Bay of Biscay against 
German submarines which began to operate 
from their newly acquired French bases in the 


28 


RADAR AND LORAN NAVIGATION DEVELOPMENTS 


fall of 1940. Just as the CH stations played an 
historic role in repelling the daylight bombing 
during the first phase of the Battle of Britain in 
the fall of 1940, so the AI Mark IV installed in the 
powerful and well-armed Beaufighter aircraft 
and guided to the enemy attackers by specially 
designed ground control of interception [GCI] 
equipment helped to defeat the Luftwaffe during 
the winter and spring of 1941. 

Both these sets operated at approximately 200 
me and had beams of exceedingly low directivity. 
This lack of directivity was a particularly seri- 
ous defect in the case of the AI Mark IV, even 
though it was partially remedied for purposes 
of accurate positioning by the use of lobe-switch- 
ing techniques. The difficulty came from ground 
reflections which, when the plane flew below a 
certain height, blanked out all echoes coming 
from horizontal distances greater than the 
plane’s altitude above ground. To realize the full 
range of the set, it was necessary to fly high 
enough so that the transmitted energy did not 
strike the ground. Because of the breadth of the 
beam, this was sufficiently high to give the enemy 
the opportunity of coming in low, beneath the 
operating altitude of the nightfighters. Although 
the enemy never fully exploited this possibility, 
and did not hit on it until it was too late, the 
threat was ever-present. 

These defects of the AI Mark IV led the Brit- 
ish to consider, even before the outbreak of war, 
the possibility of going to shorter wavelengths 
(higher frequencies) capable of producing really 
narrow beams. By the early fall of 1939 the Brit- 
ish launched two programs, one shorter-range 
and one more ambitious, to achieve these results. 
The shorter-range program was directed toward 
the development of 50-cm equipment using 
greatly perfected, but essentially conventional, 
techniques. The second program was to develop 
what hitherto did not exist ; a powerful source of 
radio-frequency energy in the neighborhood of 
3,000 me (10 cm) . 

The British had an experimental 50-cm system 
in operation early in 1940. At the time when an 
improved version of this system was about to be 
tested, in the late spring of 1940, the whole pro- 
gram was cast into the shade by the dramatic 
success of the longer-range program. As a result 
of a brilliantly conceived and swiftly executed 


research program, workers at Birmingham Uni- 
versity, in cooperation with British industry, 
had successfully designed and brought into pro- 
duction a tube capable of giving several kilo- 
watts of peak power at 3,000 me. This new type 
of vacuum tube, the resonant cavity magnetron, 
was strikingly different in form and principle 
from any previous type of tube. By opening up 
the hitherto unexplored field of microwaves, the 
magnetron may well have caused the greatest 
single revolution in the field of radio since Lee 
De Forest’s invention of the three-element vac- 
uum tube. 

2.3 EARLY HISTORY OF MICROWAVES 

Microwaves have been known from the earli- 
est days of radio, but until the development of 
the cavity magnetron by the British they were 
hardly more than scientific curiosities. They 
could not be produced by ordinary means. Con- 
ventional triode vacuum tubes can be used over a 
wide range of the radio spectrum but only by 
pushing refinements close to the limit can they 
be used to generate waves shorter than 50 cm. 
Special techniques have to be employed to gener- 
ate, transmit, and receive microwaves. Before 
1940 the principal sources of centimeter waves 
were: (1) spark-gap transmitters, (2) Bark- 
hausen-Kurz oscillators, (3) the klystron, and 
(4) the split-anode magnetron, the ancestor of 
the device developed by the British. In the years 
just before the war only the last two devices ap- 
peared to offer possibilities of operating effi- 
ciently at 10 cm or below. 

The Klystron. The klystron was developed by 
workers at Stanford University and its existence 
was first made public in 1939. The tube, which 
has been many times described, is of the so-called 
velocity-modulated variety and involves the first 
important application of resonant cavities to 
vacuum tube construction. The first tubes oper- 
ated in the neighborhood of 12 cm and gave about 
a watt of power. 

The Split-Anode Magnetron. A much more 
promising tube for the very highest frequencies 
was the so-called split-anode magnetron. This 
was derived from a simple, magnetically oper- 
ated two-element vacuum tube first described in 
1921 by A. W. Hull of the General Electric Com- 


EARLY HISTORY OF MICROWAVES 


29 


pany. This tube had very poor efficiency even for 
the generation of comparatively low frequencies. 
Shortly afterward it was discovered in Germany 
that dividing the cylindrical anode into two half- 
cylinders improved the tube as a generator of 
relatively long waves. But it was a Japanese 
worker, Kinjiro Okabe, who was chiefly respon- 
sible for demonstrating that the split-anode 
structure could turn the primitive magnetron 
into a useful (for experimental purposes) 
generator of ultra-high-frequency and hyper- 
frequency waves. 

Much work was done in all parts of the world 
in the decade following Okabe’s first papers in 
1927 to improve the magnetron. By increasing 
the number of anode segments, by careful atten- 
tion to methods of cooling the tube, and espe- 
cially by trying to improve the associated cir- 
cuit (some of the best work in this direction was 
done in American industrial laboratories) such 
progress was made in this type of tube that in 
1939 it was reported by E. G. Linder of the Radio 
Corporation of America [RCA] that an output 
of 20 w could be obtained at 8 cm with an effi- 
ciency of 22 per cent. 

Cavity Magnetron. When in England Pro- 
fessor Oliphant and his associates, Randall and 
Boot, began the search for a high-power source 
of hyperfrequency waves, they undertook two 
parallel lines of attack to improve the klystron 
and to improve the magnetron. What proved to 
be the successful solution bore to some extent 
the mark of both approaches, for it consisted in 
abandoning the split-anode construction in the 
magnetron and introducing a high-efficiency cir- 
cuit in the form of associated resonant cavities. 
By June 1940 with the collaboration of the Brit- 
ish General Electric Company they had devel- 
oped a manufacturable tube giving 10 kw of peak 
power on pulses of 10-cm energy. The order of 
magnitude of this improvement was such as to 
constitute a major revolution in the radio art. 

Waveguides. Even before the development of 
the cavity magnetron some important pioneer- 
ing work had been done in the United States on 
the properties of microwaves using the low- 
power sources then available, and some attempt 
had also been made to use them for detection pur- 
poses. The quasi-optical behavior of damped cen- 
timeter and even millimeter waves had of course 


been carefully studied by Righi, Lebedew and 
others among Hertz’s immediate followers. But 
the study of the transmission and reception of 
centimeter waves may be said to have been 
launched in 1936, the year when G. C. South- 
worth of the Bell Telephone Laboratories [BTL] 
and W. L. Barrow of MIT first reported their in- 
dependent discoveries that microwaves can be 
conducted down hollow pipes, as well as by means 
of coaxial cables, and that they could be pro- 
jected into space or picked up by means of horns 
made by flaring the ends of such waveguides. 

In the same year W. W. Hansen at Stanford be- 
gan his important work on properties of reson- 
ant cavities. Research on microwaves continued 
uninterruptedly at the Bell Laboratories, Massa- 
chusetts Institute of Technology, and Stanford, 
until the war. Fundamental research at MIT cen- 
tered on the properties of waveguides and horns 
and on the characteristics of dielectric mate- 
rials ; at Stanford it was chiefly devoted to the 
development of the klystron and the theory of 
resonant cavities; at BTL it soon included im- 
portant work on crystal mixers and other phases 
of the receiver problem. 

Continuous-Wave Applications. A number of 
independent attempts were made in the decade 
before the war to use microwaves for detection 
purposes. The Signal Corps Laboratories, and to 
lesser extent the Naval Research Laboratory 
[NRL], experimented with c-w (continuous 
wave) methods of detection with microwaves be- 
fore putting their full effort on longer-wave 
pulse radar. The RCA-Victor Division of RCA 
experimented with c-w detection in cooperation 
with the Army and later had some success with a 
pulse detection system on 3,000 me. In 1936 the 
General Electric Laboratories [GE] published 
an account of successful detection of objects 
with microwaves by means of the doppler effect 
using c-w radiation. Similar experiments were 
made in Germany and in France. The French 
had a microwave set on the Normandie as an 
obstacle detector. The low-power split-anode 
magnetron was the source of radiation in nearly 
all these cases and the ranges obtained were 
prohibitively short. 

In America most of these microwave detection 
efforts had either been abandoned or severely 
curtailed by 1940. However, an active program 


30 


RADAR AND LORAN NAVIGATION DEVELOPMENTS 


of aircraft detection using the klystron as the 
source of c-w radiation was in progress at San 
Carlos, California. This was a joint project of 
the Stanford Physics Department and the Sperry 
Gyroscope Company. Similar work was started 
shortly thereafter in the Department of Electri- 
cal Engineering of MIT. Here the communica- 
tions division under Professor E. L. Bowles had 
been experimenting with a radio blind-landing 
project using ultra-high-frequency techniques 
as developed by Barrow and his co-workers. 
Early in 1939 a straight-line glide-path scheme 
was tried using the klystron as the source of 40- 
cm waves. Later in 1939, the MIT group entered 
into an agreement to conduct a research pro- 
gram, under the sponsorship of the Sperry Gyro- 
scope Company, pointing to the development of 
an aircraft detecting device on 10 cm using the 
klystron. A crude c-w detection device using 
three horns (one transmitting horn and two re- 
ceiving horns) was set up on a movable platform 
mounted on a Sperry searchlight base. 

Early in 1939 Alfred L. Loomis, New York 
lawyer and scientist, began work at his private 
Tuxedo Park laboratory on the general field of 
ultra-high-frequency work using the klystron, 
and later in the year contributed funds to sup- 
port a program of microwave propagation re- 
search at MIT. In the spring of 1940, Loomis 
made arrangements with E. L. Bowles for a pro- 
gram of microwave detection at Tuxedo Park in 
cooperation with the MIT group. An experi- 
mental set using an 8.6-cm klystron as the trans- 
mitting source to detect objects by the doppler 
effect using c-w radiation was built during the 
summer of 1940 by Loomis and his co-workers. 

2.4 the INAUGURATION OF THE NDRC 
RADAR PROGRAM 

It was clear from the time the first plans were 
made in June 1940 for a civilian war weapons 
program that NDRC should concern itself with 
some phase of radio detection. The earliest pro- 
posals provided that a section of K. T. Compton’s 
Division D should be devoted to detection, 
broadly conceived, including work on search- 
lights, acoustical detection, infrared and micro- 
waves. The decision to limit the detection work 
to the field of microwaves was made almost at 
once. 


Since there was as yet no knowledge of the 
British magnetron, such a decision fulfilled to a 
fault the condition that the civilians should con- 
centrate on long-range projects deemed too spec- 
ulative for the Service laboratories in time of 
war. Furthermore it was in harmony with the 
suggestions submitted to Vannevar Bush by the 
Armed Services late in June. These suggestions 
emphasized the importance of general studies of 
pulse transmission and reception and of basic 
research in the hyper-frequency field. The Air 
Corps, the suggestions revealed, was especially 
interested in certain problems of instrumentation 
(fog and haze penetration and the possibilities 
of reconnaissance and bombing through the 
overcast) where the solutions undoubtedly lay 
in the ultra-high-frequency or hyper-frequency 
radio fields. 

This decision resulted in a necessary and natu- 
ral division of effort. It left the field of longer- 
wave radar in the hands of the Army and Navy 
personnel who had developed it, and who were 
deeply involved in improving it and shepherding 
it through production. Since all the detection ex- 
periments undertaken in civilian laboratories in- 
dependently of the Armed Services had been in 
the field of microwaves, it put the civilians to 
work where they had already acquired some ex- 
perience. 

Executive Organization 

The man selected by Compton to organize a 
section devoted to detection, Alfred L. Loomis, 
was one of the most energetic and enthusiastic 
of these microwave pioneers. Loomis had close 
personal and scientific connections with Bush 
and Compton. He was a trustee of MIT and of the 
Carnegie Institution. He had generously contrib- 
uted from his own pocket to the support of micro- 
wave research, in the Department of Electrical 
Engineering at MIT; and as we have just men- 
tioned he was at this time conducting some 
microwave experiments, in cooperation with the 
MIT group, at his own laboratory at Tuxedo 
Park. Bush and Compton were following this 
work closely. 

Loomis chose as his first associates on what 
came to be called Section D-1 of NDRC, or the 
Microwave Committee, Ralph Bowen, director of 
radio and television research at BTL, and two 


THE BRITISH TECHNICAL MISSION 


31 


other men who had experience with the micro- 
wave field: E. L. Bowles of MIT, who became 
secretary of the committee, and Hugh H. Willis, 
research Director of the Sperry Gyroscope Com- 
pany. These four men held their first meeting on 
July 14, 1940. During the next few months the 
following persons were added to the committee : 
R. R. Beal, Director of Research of RCA ; George 
F. Metcalf of the General Electric Company 
[GE] ; J. A. Hutcheson of the Westinghouse 
Electric and Manufacturing Company ; and 
Ernest 0. Lawrence, professor of physics 
and director of the radiation laboratory for 
nuclear physics at the University of California 
at Berkeley. It was a group experienced in the 
administration of scientific research, well versed 
in current radio developments, well placed to 
coordinate the scattered work in this new field, 
and well fitted to administer the funds soon to 
be placed at its disposal. 

Objectives j 

The committee defined its objectives in these 
terms : “So to organize and coordinate research, 
invention and development as to obtain the most 
effective military application of microwaves in 
the minimum time.” The next two months were 
spent in learning what the Armed Services had 
accomplished in radio detection behind their veil 
of secrecy, and surveying the field of microwave 
research to determine what developments seemed 
most promising. 

The survey revealed that much interesting 
work was in progress in various commercial and 
university laboratories, but that there was no 
sign that a vacuum tube was anywhere in pro- 
duction or development which might give ade- 
quate power on the very short wavelengths which 
the committee had decided would be most desir- 
able, namely, 10 cm or below. 

Only two vacuum tubes seemed to offer possi- 
bilities below one meter, the klystron, already 
being commercially developed b> Sperry; and 
the so-called resnatron, a multi-element vacuum 
tube developed at the University of California. 
The possibilities of the latter tube were carefully 
investigated by the committee, and it was found 
capable of giving about a kilowatt of peak power 
at about 45 cm. There was reason to expect that 
the frequency and the power could both be raised 


by further development, although there was 
little promise that it would yield a source of 
energy at wavelengths as short as 10 cm. On the 
recommendation of the Microwave Committee, 
the NDRC let its first microwave contract on 
November 1, 1940, with the University of Cali- 
fornia for the development of a higher-power 
and higher-frequency resnatron. 

2 5 the BRITISH TECHNICAL MISSION 

This was the rather uncertain prospect when 
the British Technical Mission, headed by Sir 
Henry Tizard, arrived in Washington and began 
conversations with the representatives of the 
U. S. Army and U. S. Navy early in September 
1940. In these discussions each nation divulged 
to the other the details of its secret radar devel- 
opments. 

About the middle of September, the way was 
cleared to have the appropriate members of 
the Tizard Mission meet the section leaders of 
NDRC. By special arrangement, the Mission was 
empowered to treat with the civilian scientists 
on the same terms as with the Armed Services. 

The first contact between the radar members 
of the Mission and representatives of NDRC took 
place at an informal evening conference held at 
the Wardman-Park Hotel late in September. The 
first extended talks took place over the weekend 
of September 28th when J. D. Cockcroft and 
E. G. Bowen, the radar specialists on the Mission, 
met with several members of the Microwave 
Committee and of NDRC as guests of Alfred 
Loomis at Tuxedo Park. It was on this occasion 
that the British explained their long-range ob- 
jectives in radar (especially the importance to 
them of a microwave airborne set without the 
defects of the AI Mark IV) and showed the 
committee members the sample cavity magne- 
tron they had brought with them as their prize 
exhibit. 

U. S. Production of Magnetron 

During the first week of October, the British 
representatives, with the official approval of the 
United States authorities, disclosed the cavity 
magnetron to engineers of BTL, the organization 
they had selected to manufacture it in this coun- 
try. On Sunday, October 6, the tube was operated 


32 


RADAR AND LORAN NAVIGATION DEVELOPMENTS 


for the first time in this country in the presence 
of Bell engineers and work on duplicating the 
device began the following day at BTL. 

Meanwhile the disclosure of the magnetron 
had exerted a profound effect upon the members 
of NDRC and Section D-1. The new tube re- 
moved the chief obstacle to a successful develop- 
ment program in the microwave field. A major 
breach had suddenly been opened in the line 
through which the reserve strength of American 
university and industrial resources could pour. 
With energetic exploitation of this initial stroke 
of good fortune, microwave radar could be de- 
veloped in time to be useful in the war. This was 
the article of faith, and it was not universally 
shared in all quarters, upon which the Micro- 
wave Committee with the prompt and active 
encouragement of Bush and Compton based their 
subsequent decisions. 

During the first two weeks of October a series 
of important conferences was held in Cambridge, 
New York City, and Tuxedo Park in the course 
of which the main outlines of a concrete program 
were formulated by the Microwave Committee. 
E. G. Bowen, who was remaining behind after 
the departure of the Tizard mission, took an 
active part in these discussions, by describing 
the British Air Ministry’s radar research organ- 
ization, and by helping to lay down the specific 
objectives for a microwave program. 

There was general agreement that a central 
laboratory under civilian direction should be 
set up at once, staffed, in the manner of Britain’s 
AMRE, as much as possible by research physi- 
cists from the universities of the country. This 
policy had proved extremely successful in Eng- 
land. It was at first felt when the possibilities 
were canvassed that the laboratory should be 
set up at Bolling Field, Washington, D. C., where 
a large heated hangar with associated labora- 
tories would be erected by the U. S. Army. 

2.6 the first three PROJECTS OF THE 
MICROWAVE COMMITTEE 

It was also decided, largely on the basis of 
British need, to concentrate on three projects, 
not greatly different from those proposed by the 
American Armed Forces. Two out of three were 
to use the cavity magnetron. Project I, and the 


project of greatest urgency from the British 
point of view, was to build a 10-cm AI system. 
Project II, also to be entrusted to the National 
Research Council of Canada, was to develop a 
precision gunlaying radar capable of great accu- 
racy. Project III was to design a long-range 
navigation device, one in which the aircraft sent 
out no signals, but which, when a plane was over 
enemy territory some 500 miles away from its 
base, could tell the navigator his position within 
a quarter of a mile. 

Definite steps were agreed upon to launch 
Project I. Bowen, who was England’s outstand- 
ing authority on airborne radar, drew a block 
diagram of component parts necessary for a 
microwave AI system, and from his knowledge 
of the operational requirements, laid down the 
specifications the equipment should be designed 
to meet. For experimental purposes it was de- 
cided to ask the principal electronic and electri- 
cal concerns to design and supply a few units of 
each of these components. These proposals were 
officially agreed upon at an important full-dress 
meeting of the Microwave Committee held in 
Washington on October 18 and attended by Bush, 
Compton, and several high-ranking Army and 
Navy officers. 

As a result of a last minute decision arrived 
at two days before, the Microwave Committee 
at this meeting unanimously approved plans to 
establish the microwave laboratory at MIT. 
Various factors entered into this decision. Some 
delays had been encountered in getting matters 
underway at Bolling Field, and what was doubt- 
less more important, it was pointed out that the 
NDRC was not empowered to administer its own 
laboratories but should operate through contract 
with existing institutions. Work on microwaves 
being already in progress at MIT, the atmos- 
phere should be a congenial one. When Compton 
arrived in Washington on October 17 he was 
confronted with the proposal, agreed upon in 
conference the previous day by Bush, Jewett, 
Loomis, and Bowles, that MIT offered a better 
prospect than Bolling Field. He was persuaded 
to give his approval and to telephone MIT to 
ascertain if the required space could readily be 
made available. 

On October 25, 1940, the NDRC approved the 
program as submitted to it by the Microwave 


FOUNDATION OF THE RADIATION LABORATORY 


33 


Committee. This covered the five development 
contracts for the components and the contract 
with MIT which was later signed on February 
5, 1941. The sum of $455,000 was allocated for 
the first year of the laboratory's existence.’* How 
modest this appropriation was should be evident 
from that fact that it envisaged a laboratory of 
only fifty persons, including technical assistants, 
mechanics, and secretarial help. 

2.7 FOUNDATION OF THE RADIATION 
LABORATORY 

E. 0. Lawrence had actively joined the work 
of the Microwave Committee early in October 
in response to an urgent summons from Bush. 
The importance of his addition to the committee 
was evident as soon as it was decided to draw 
mainly upon American academic physicists in 
finding personnel for the new laboratory. He 
alone, perhaps, of the members of the Microwave 
Committee could readily have enlisted the sup- 
port of his colleagues in the American Physical 
Society in a project the details of which could 
not at first be disclosed. His first success, soon 
after his arrival in the East, was in inducing 
L. A. DuBridge, Chairman of the Physics De- 
partment and since 1938 Dean of the Faculty of 
Arts and Sciences of the University of Roches- 
ter, to accept the post proffered him, by the 
Microwave Committee and by Compton, as head 
of the microwave laboratory. Lawrence also 
made visits to colleagues at Harvard, Princeton 
and other Eastern institutions, while DuBridge 
went to the University of Indiana where a small 
group of physicists from several Midwestern 
universities were meeting in an interdepart- 
mental seminar. These men were sounded out in 
general terms. 

More active recruiting took place in Cam- 
bridge by Lawrence, DuBridge, and the Micro- 
wave Committee during the week of October 
28-31 when a conference on applied nuclear phy- 
sics brought to MIT some 600 physicists from 
all parts of the country. At the conclusion of the 
conference most of those who had been ap- 
proached left Cambridge, but a small group re- 
mained behind, and strengthened by personnel 
chosen from Harvard and the Massachusetts 
Institute of Technology, began a general discus- 
^ Under the contract NDCrc-53. 


sion of certain key microwave problems and took 
steps to occupy the space set aside for the new 
laboratory in the wing of the main MIT building 
occupied in part by the Department of Electrical 
Engineering. 

On Monday, November 11, there was held the 
first general group meeting of the laboratory 
personnel. At this meeting, and one held the fol- 
lowing day, attended by Alfred Loomis and E. 0. 
Lawrence, the main outlines of the laboratory 
organization were agreed upon. Research prob- 
lems were parceled out among seven technical 
sections concerned with developing or improv- 
ing the chief components of the system. Section I 
was concerned with pulse modulators. Section II 
with transmitter tubes. Section III with anten- 
nas, Section IV with receivers. Section V with 
problems of microwave theory. Section VI with 
cathode-ray tubes, and Section VII with work on 
the klystron. A final section. Section VIII, the 
coordination section, was charged with the tech- 
nical integration of equipment being manufac- 
tured or designed for the use of the laboratory. 

By the middle of December the organization 
consisted of some 35 persons. About half of the 
promised space had already been occupied and a 
roof laboratory— a wooden penthouse covered 
with grey-green tarpaper— had been erected on 
the roof of MIT Building 6, and a second story 
was being added. The personnel consisted of 
about 30 physicists, three guards, two men in 
charge of the stockroom and the purchase of 
supplies, and one secretary. The laboratory was 
placed under the supervision of an executive 
committee consisting of Loomis and Bowles of 
the Microwave Committee, L. A. DuBridge, the 
director of the laboratory, and Melville Eastham, 
president of the General Radio Company, the 
business manager. It had already received the 
name of “Radiation Laboratory," selected be- 
cause it concealed, yet in ironical fashion, ex- 
pressed the functions of the laboratory. The 
adoption of the name used by Lawrence’s cyclo- 
tron laboratory at Berkeley, suggested the natu- 
ral hypothesis that this group of nuclear physi- 
cists was engaged in nuclear physics, then 
deemed a harmless and academic occupation. 

BTL delivered their first five magnetrons pre- 
cisely on schedule on November 18. The first 
units of the other components began to arrive 


34 


RADAR AND LORAN NAVIGATION DEVELOPMENTS 


shortly after. It was recognized from the begin- 
ning that these components were only a starting 
point. Work was coordinately begun on testing 
and adapting the delivered items, on design of 
new components suitable for use in an aircraft, 
and on assembling a first working microwave 
radar with the equipment available. 

On the afternoon of December 16, a planning 
meeting was held at the laboratory and a sched- 
ule to be met was laid down. This provided that 
by January 6 a microwave system should be 
working on the roof ; that by February 1 equip- 
ment should be working in a fiying laboratory, a 
B-18 plane to be supplied by the Army ; and that 
by March 1 a system should be working in an 
A-20-A aircraft, which at that time was the most 
likely choice for a nightfighter. A group charged 
with the assembly of the system was at once 
set up. 

First Experimental System 

During the last two weeks of December the 
first experimental radar system was assembled 
in the roof laboratory largely from the com- 
ponents supplied with such admirable dispatch 
by the commercial concerns. The system had a 
separate antenna for transmitting and for re- 
ceiving, for the problem of a duplexer, or what 
the British referred to as a transmit-receive 
[TR] box, to permit the use of the same antenna 
for transmitting and receiving, had not yet been 
solved. This system was first successfully oper- 
ated on January 4, 1941, two days ahead of sched- 
ule, and picked up echoes from the buildings of 
the Boston skyline across the Charles River. 

Single Parabolic Antenna Trials— In order to 
design a system for use in an aircraft, it was im- 
perative that it operate with only a single an- 
tenna. Yet with a single parabola without a du- 
plexing or switching device, or at least some pro- 
tection for the receiver crystal, the main trans- 
mitted pulse would burn out the receiver crystal. 
While various solutions were being tried, it was 
discovered early in January that a klystron used 
as a preamplifier tube, would serve effectively as 
a buffer for the crystal. While only a partial so- 
lution to the TR box problem, it permitted the 
roof system to be operated with a single para- 
boloid on January 10. Before the end of the 
month an almost identical system with its com- 


ponents shock-mounted was operating in a 
wooden mock-up intended to represent the nose 
and front gunner’s compartment of a B-18. 

As yet, this system had only picked up ground 
echoes. Attempts to pick up aircraft signals had 
failed and some observers doubted that the sys- 
tem was capable of performing this essential 
feat. As a result of frantic efforts and some last- 
minute improvisation, aircraft signals were ob- 
served on February 7 in time to be reported by 
telephone to a gloomy session of the Microwave 
Committee which DuBridge was attending in 
Washington. The report of this success changed 
the mood of the meeting which voted confidence 
in the AI program. 

Development of Airborne System 

Between February 13 and March 5 the system 
that had been in the mock-up was worked over 
and modified for installation in the plane. On 
March 6-7 it was installed in a B-18 plane, 
equipped with a special Plexiglas nose trans- 
parent to hyperfrequency radiation, which had 
been fiown up from Wright Field by an Army 
crew. The equipment was first fiown on March 
10. Its performance was steadily improved dur- 
ing the rest of the month. 

On March 27 there took place a flight in the 
B-18 with several laboratory scientists aboard 
which had important consequences for the lab- 
oratory. The equipment performed admirably, 
and for what was probably the first time an air- 
borne microwave radar was tried out for aircraft- 
to-surface vessel [ASV] purposes. Tests on a 
10,000-ton ship gave strong signals, and the “sea 
return,” i.e., interfering echoes from the surface 
of the water, was much less than had been feared. 
Encouraged by this success, the plane was flown 
to New London to look for submarines operating 
near that base. There the pilot made successful 
runs on a surfaced submarine and the men found 
that from an altitude of 500-1,000 feet strong 
signals were obtained at a distance of 3 miles. 

The first flight of the experimental AI equip- 
ment on March 10 can be taken to mark the end 
of the first phase of the laboratory’s history. On 
this date the Microwave Committee submitted 
its first report on the laboratory to Bush, describ- 
ing the progress that had been made in the AI 


FOUNDATION OF THE RADIATION LABORATORY 


35 


development, upon which most of the Laboratory 
effort was concentrated, and the less extensive 
results of Project II, gunlaying, and Project III, 
long-range navigation, to be discussed in sub- 
sequent text. 

Up to the month of March the main effort at 
MIT-RL had been to get a plane in the air with 
radar aboard, and to meet as closely as possible 
the schedule laid down in mid-December. This 
phase of the laboratory's history was now closed, 
and there began a period of greatly expanded 


and diversified effort. The laboratory’s attention 
was still primarily directed toward a perfected 
AI equipment suitable for operational aircraft. 
This was predicated chiefly upon the successful 
design of new and improved components. But 
there was increased activity in Projects II and 
III and additional development along two main 
lines: (1) new applications of the 10-cm AI 
equipment, especially those involving the use of 
microwave radar over water, and (2) develop- 
ment of radically new types of radar. 



PART II 


PROGRAM OF RADIATION LABORATORY 
AND ASSOCIATES 



Chapter 3 


TECHNICAL PROGRAM OF THE RADIATION LABORATORY 


3.1 MICROWAVE RESEARCH 

U nquestionably the most important aspect 
of the laboratory’s effort during the first 
year, and almost equally vital in the years that 
followed, was the development of improved com- 
ponents and the steady growth of knowledge of 
the properties of microwaves: how to produce 
them, carry them along coaxial cables or wave- 
guides, receive them, amplify them, and display 
them ; how they are propagated through the at- 
mosphere and how they behave under different 
meteorological conditions. 

A word should be said about the manner of 
work. The laboratory was loosely and informally 
organized, small enough for constant interaction 
of the various parts, and even for frequent ex- 
change of personnel. The spirit and morale were 
very high. The lines separating the different sec- 
tions were anything but formal barriers. Men 
drifted across them freely, to aid one another in 
a tight spot, even sometimes to trespass to good 
effect in someone else’s preserve. It was a picked 
group, fully conscious of its undiluted strength, 
as yet untroubled by problems of production and 
higher diplomacy, unencumbered by administra- 
tive routine. 

These men shared with the industrial labora- 
tories, chief among them the Bell Telephone Lab- 
oratories [BTL], the experience of laying the 
foundations of a new engineering art. The con- 
ditions and objectives of research were widely 
different from what most of the men had been 
accustomed to. It was applied science ; and it was 
also wartime science. Especially during the first 
year the men relied upon empirical investigation 
of the cut-and-try variety, guided by their theo- 
retical training and insight, but without benefit 
of much practical experience in radio engineer- 
ing. The rediscovery, en route, of familiar engi- 
neering dodges was not an uncommon experi- 
ence. They felt, on the other hand, that they were 
free from a heavy load of accumulated practices 
of radio engineering not always adaptable to 
this new field. The wartime urgency of their 
work meant that a wholly logical, planned attack 


on a problem as in peacetime, was almost never 
feasible. Speed was the all-important considera- 
tion and there was no time for leisurely theo- 
retical exploration or fundamental research un- 
derlying a given problem. Most of the knowledge 
was acquired by building something as quickly 
as possible and trying it out. Theoretical knowl- 
edge grew pari passu to be plowed back into the 
work at a later date. Hence the importance of the 
various experimental systems soon scattered 
throughout the laboratory. Experimentation 
consisted mainly in trying out new components 
and new ideas as swiftly as possible in the ex- 
perimental systems on the roof or in the B-18. A 
roof system group was established early in Feb- 
ruary for conducting such testing and for the 
general improvement of microwave system de- 
sign. 

3 2 DEVELOPMENT OF IMPROVED 
COMPONENTS 

^ ^ ^ Experimental Systems 

The first systems were frankly experimental, 
intended to educate the laboratory members in 
the new art, and to help them obtain some gen- 
eral familiarity with the properties of micro- 
waves. All the earliest systems were assembled 
almost entirely from the components supplied by 
industrial concerns under the first contracts. 
These components in some instances had been 
considerably modified and changes in them were 
constantly being made. A rebuilt Westinghouse 
pulse modulator, a Bell copy of the British mag- 
netron, a Sperry paraboloid and scanning gear, 
a receiver consisting of a BTL crystal mixer, a 
grounded-grid triode local oscillator, together 
with an RCA intermediate frequency amplifier ; 
these found their way into all the early experi- 
mental systems. The only component in the early 
systems designed and built entirely by the lab- 
oratory was the very important synchronizer 
unit, of which about twenty were built by hand 
in the first few months. It was used to provide 
triggering pulse to the modulator, banking 


39 


40 


TECHNICAL PROGRAM OF THE RADIATION LABORATORY 


pulses to the receiver, and to synchronize the 
sweep circuits for the cathode-ray tube. 

Only the briefest outline is possible here of the 
complex activity which produced, within less 
than a year and a half, a satisfactory, if primi- 
tive, operative microwave radar system. Work 
began on the development of components during 
the first days of the laboratory. 

3.2.2 Development of Components 

Magnetron 

The essential features of the 10-cm magnetron 
were not substantially altered. The development 
of power-measuring techniques and of spectrum 
analyzers made it possible to understand the po- 
tentialities of the tube and to get much more 
power out of it than the British had been led to 
expect. The introduction of a technique called 
“strapping,’^ which the laboratory learned from 
the British in the fall of 1941, greatly increased 
the stability and the efficiency of the magnetron. 
Although no wholly satisfactory theory of mag- 
netron operation was evolved, much was learned 
about the modes in which the tube can oscillate. 

The most important achievement — and one 
upon which the magnetron group concentrated 
from the very first— was the development of a 
magnetron operating on 3 cm. This was success- 
fully accomplished in the spring of 1941 with the 
adoption of some novel changes in magnetron 
design. In both the 10-cm and 3-cm work the lab- 
oratory was greatly aided by a vacuum-tube 
model shop facility provided by the Raytheon 
Manufacturing Company in Newton, Massa- 
chusetts. Here a handful of tube experts pro- 
duced experimental magnetrons, modulator 
tubes, etc., following suggestions and drawings 
submitted by MIT-RL. Raytheon operated on a 
subcontract from MIT’s Division of Industrial 
Cooperation, MIT being reimbursed under the 
OSRD prime contract OEMsr-5. 

Pulse Modulator 

The pulser or pulse modulator, supplied by 
Westinghouse and used in the early experimental 
systems produced pulses of the required length 
and repetition rate, but was too wasteful of 
space, weight, and power to be a satisfactory de- 


sign. As early as November 8, 1940, the pulse- 
modulator problem was discussed with a view to 
developing a unit suitable for aircraft use. Two 
important developments of the modulator group 
during the winter of 1940-41 laid the founda- 
tions for the later art of radar pulse modulators. 
The first of these was the development of a “boot- 
strap” cathode-follower circuit. The second was 
the discovery of the pulse-forming network. 
These were important elements in the design of 
the so-called service modulator and laboratory 
modulator embodying these developments, both 
of which were manufactured during the year by 
Raytheon. The use of the network did much to 
improve the pulse shape and later became the 
basis of the high-power modulator using the 
pulse-forming line with rotary spark gaps. 

An important contribution to the work of the 
modulator group was the development of testing 
equipment (r-f envelope viewers and synchro- 
scopes) which permitted the study of pulse 
shapes. Special adaptations of the basic circuits 
were used in designing the modulators for vari- 
ous laboratory systems intended for production. 
Work was begun late in 1941 on the high power 
modulators and on the development of modula- 
tors using oxide-coated cathode output tubes, 
among them a light-weight pulse modulator man- 
ufactured by the Stromberg-Carlson Company, 
later referred to as the Navy standard pulser. 

Antenna Design 

Improvements in antenna design consisted 
largely in finding the proper way of feeding r-f 
energy to a standard parabolic reflector, and de- 
termining the optimum focal length and the 
proper design and proper matching of the radiat- 
ing dipoles. The effort was concentrated upon 
getting a high-gain pencil beam with low side 
lobes, without introducing very novel reflector 
dish design. 

R-F AND I-F Problems in Receiver Design 

Use of I-F. The receiver problem divided itself 
into the r-f and the i-f problems. The earliest i-f 
receiver strips from BTL and RCA had been de- 
signed on the basis of television experience and 
were only a first approximation of what was re- 


DEVELOPMENT OF IMPROVED COMPONENTS 


41 


quired for microwave radar. In its broad out- 
lines, the development was conservative and 
there was no departure from the basic super- 
heterodyne principle ; yet there were fundamen- 
tal departures in circuit design which made it 
possible to design high-gain and broad band- 
width receivers with proper transient response. 
The novel problem in radar was to build receiv- 
ers that could tolerate unbounded signals and 
escape paralysis from the effects of the main 
transmitted impulse. 

R-F Receiver-Detectors, The receiver r-f prob- 
lem was part of the broader problem of handling 
r-f energy on these frequencies. The answer to 
the question as to which first detector, whether 
a crystal mixer or a grounded-grid triode was 
better, hinged in great part upon a solution of the 
duplexing or TR box problem. The earliest lab- 
oratory experimental systems used a crystal de- 
tector, then shifted over to the use of a BTL 
grounded-grid triode, and finally settled on the 
crystal mixers which became standard for all 
subsequent microwave radar. This was both be- 
cause crystals had finally nosed out tube detec- 
tors in the race for sensitivity and because the 
solution of the TR box problem gave adequate 
protection to the crystal. 

R-F Coaxial Lines and Test Equipment. The 
earliest r-f work at the laboratory, in connection 
with designing a 10-cm AI system, was centered 
on three main problems : to design improved co- 
axial lines and line components such as tuners 
and rotary joints; to evolve measuring equip- 
ment to test the components under development ; 
and to solve the TR-box problem. The coaxial line 
was first radically improved by designing a 
beaded line using a particular nonuniform spac- 
ing of the polystyrene beads, and finally by 
adopting the use of brass stubs instead of beads 
to support the inner conductor. To meet the need 
of measuring equipment, standing-wave detec- 
tors, wavemeters and wattmeters were devel- 
oped and improved. In the spring of 1941 the 
laboratory designed a successful and rugged 
spark-gap TR box which was followed by the 
adoption and improvement of the British so- 
called soft Sutton Tube TR. A further improve- 
ment in the duplexing system was the adoption 
of '‘preplumbing.” This consisted in the pre- 
selection of the proper length of transmission 


line between the magnetron and the TR box, so 
as to insure without special tuning devices, the 
minimum loss in received signal. 

Adoption of Waveguide Transmission Lines. 
With the appearance of the first 3-cm magne- 
trons in the spring of 1941 the whole art had to 
be translated to this new wavelength. Wave- 
guide transmission lines were adopted instead of 
coaxial lines, which would have to be prohibi- 
tively small. The properties of waveguides had 
to be carefully studied, and a complete new set of 
components, such as tuners, rotary joints, wave- 
guide “T's” and angles, fiexible waveguide, etc., 
had to be developed. Receiver r-f components, 
crystals and local oscillators, and a TR box for 
the new wavelength all were needed. The impossi- 
bility of “preplumbing” the 3-cm magnetrons at 
this period led to the development of a so-called 
anti-TR, another glow-discharge device inserted 
in the line to keep the transmitter from absorb- 
ing any appreciable amount of the received sig- 
nal. 

Indicator Tubes 

Preliminary Indicators. The key problem of 
the indicator group was the cathode-ray tube it- 
self. The earliest indicator tubes used by the lab- 
oratory were those supplied by RCA under the 
first contract. Although they served a useful ex- 
perimental purpose they were recognized as only 
a stop gap. They were large electrostatically de- 
fiected tubes with a 12-in. face and a screen that 
consisted of a single layer of phosphor having 
only slight persistence. 

The British representatives had described in 
general terms the importance of having long- 
persistence tubes, though they had been unable 
to give anything but general information of re- 
ported British developments along this line. 
They explained however that the British used a 
duplex-layer screen composed of two phosphors, 
an inner layer emitting short fiashes of blue and 
ultraviolet light when electrons impinged on the 
surface, and an outer layer emitting orange light 
with a slow decay when activated by the light 
from the inner screen. NDRC contracts were let 
to the General Electric Company [GE] and to 
RCA Victor early in 1941 to develop long-delay 
cathode-ray tubes along these lines. The two re- 


42 


TECHNICAL PROGRAM OF THE RADIATION LABORATORY 


search laboratories worked closely together in 
cooperation with the MIT-RL indicator section 
which served principally in the role of a coordi- 
nating and testing center for research and later 
for production control. Delicate techniques were 
developed for measuring the characteristics of 
the phosphors in tubes submitted by GE and RCA. 

Development of Standard Tubes. By the sum- 
mer of 1941 what have become essentially stand- 
ard tubes were adopted by the laboratory. These 
were for general use, but were especially suited 
to airborne installations, being smaller and more 
compact than earlier experimental models. They 
were tubes with a flat face, and a duplex-layer 
persistence screen. Seven-inch and 5-inch tubes 
were designed, in which the electron beam was 
focused and deflected by a magnetic field, instead 
of by electrostatic means. Large-scale produc- 
tion was begun at GE and RCA. 

For AI work these tubes were adapted to pro- 
duce so-called Type C scan, with a rectangular 
image in which elevation is plotted against 
azimuth and a Type B scan giving range against 
azimuth. The improved cathode-ray tubes were 
also used for the plan-position indicator [PPI] 
built in the laboratory during 1941. The work 
was undertaken on the basis of general informa- 
tion about the British PPI development, but 
without specific design data. This type of indi- 
cator has a linear sweep that takes its origin at 
the center of the tube. The sweep is rotated in 
synchronism with a rotating paraboloid. The 
laboratory’s first PPI, which was probably the 
earliest built in this country, was a magnetically 
focused and deflected tube with coils which were 
mechanically rotated. It was developed for an 
experimental shipboard system on the USS 
Semmes. An electrostatically deflected tube was 
built at nearly the same time for the earliest ex- 
perimental 10-cm ASV system. By the middle of 
1942 two types of PPI indicators had been de- 
vised : one with a mechanically rotated coil and 
one with a fixed coil using selsyns to provide the 
proper vector components. 

Synchronizer Unit 

Late in the year an important change was 
made in the synchronizer unit. It was incor- 
porated into a single box with the indicator cir- 
cuits to produce the unit called the control central 


or indicator central. This important component 
became a central timing device, the heart of the 
modern radar system. It establishes the pulse re- 
currence rate, starts the modulator, which in 
turn operates the magnetron, and produces 
sweep voltages for the indicator tubes that are 
synchronous with the transmitter pulses. Much 
attention was paid to developing circuits for a 
high-speed 1-mile sweep. At about this same time 
circuits were devised to introduce range markers 
electronically on the sweeps. 

3 3 WHAT HAPPENED TO PROJECT I: AI 

Demonstration of 
Experimental AI Equipment 

In a conference held on January 17, 1941, at 
Wright Field, attended by MIT-RL physicists 
and British representatives, the Army spokes- 
men expressed their doubts as to the desirability 
of installing AI-10 equipment in the Douglas 
A-20-A attack bomber, as had been tentatively 
suggested, and instead, made known their pref- 
erence to have the equipment designed for in- 
stallation in the P-61, then in the mockup stage 
at the Northrup plant. It was agreed that a trial 
installation in an A-20-A might serve as an in- 
termediate step. In February the Army asked 
MIT-RL to provide equipment for 15 experimen- 
tal P-61’s and for one nightfighter version of 
the Douglas XA-26-A attack bomber. 

The B-18-A equipment, improved by general 
tinkering and by the incorporation of the Law- 
son TR box and the addition of better indicators, 
was demonstrated to Sir Hugh Dowding, Com- 
mander of the RAF Fighter Command. During 
the month of July this experimental system was 
flown to Wright Field and demonstrated to the 
U. S. Army Air Forces. 

3.3.2 Development and Production 
of SCR-720 

Early in April, soon after the initial flights of 
this flying laboratory, a so-called A-20 version of 
the AI equipment was assembled in a mockup in 
the roof laboratory. Late in May, this system was 
sent at the U. S. Army’s request to BTL in the 
care of two MIT-RL men who were loaned to 
BTL for the rest of the year to help engineer a 


<;;e;BrR|lE3 


PROJECT II: FIRE CONTROL AND AUTOMATIC TRACKING— SCR.584 


43 


finished set. From this cooperation emerged the 
first production AI set, the SCR-520, of which 50 
were produced by the Western Electric Company 
before the end of 1942. This set, of which only 
about a hundred were ever produced, was modi- 
fied shortly after Pearl Harbor into the first pro- 
duction ASV set, the SCR-517 or ASC which was 
produced in considerable numbers. Its much im- 
proved lineal descendant. Western Electric’s 
SCR-720, in which BTL engineers incorporated 
the latest improvements in 10-cm art, actually 
became America’s standard nightfigher radar 
installed in the P-61’s, the much publicized Black 
Widows. The 720’s began to come off the produc- 
tion lines in the spring of 1943 and several thou- 
sand had been delivered by D-Day. 

A second system destined for an A-20 aircraft 
was completed at MIT-RL in June 1941. The 
plane that was being modified to receive it had 
not yet been delivered, so the set was taken to 
Wright Field where it was demonstrated for sev- 
eral weeks in a trailer parked on a nearby hill. 
The system was finally installed in the A-20 
plane and flown for the first time late in Septem- 
ber and handed over to the Army for tactical 
experiments at Mitchel Field. Shortly after the 
attack on Pearl Harbor this plane was flown to 
the West Coast where, it is reliably reported, it 
constituted America’s entire nightfighter pro- 
tection in the event of an invasion of the Pacific 
Coast. 

In June of 1941 an American AI-10 system 
prepared for installation in a Canadian Boeing 
247D was taken to England by an MIT-RL rep- 
resentative for comparison with the British ex- 
perimental AI-10 which had reached approxi- 
mately the same stage of development. The im- 
portant discovery was made during these com- 
parative tests that the American transmitter 
gave much more power than the British, but that 
the British had developed a more sensitive re- 
ceiver. The performance of these two systems 
was therefore roughly comparable. Great im- 
provement resulted when the best features of 
both systems were subsequently combined. The 
Americans adopted the British-type crystal 
mixer in place of the tube mixer and brought 
back the soft Sutton Tube TR box. 

During this period of testing, the laboratory 
began procurement of the components for the 


fifteen P-61 sets and for ten comparable sets 
which the British had requested for installation 
in Beaufighter aircraft for the RAF. As the year 
drew to a close it was increasingly evident that 
Service interest in “crash” procurement of AI 
equipment was less than acute; the production 
of the P-61’s had been seriously delayed and they 
could be taken care of by production radar 
equipment when it appeared; the British also 
showed signs of losing interest in AI, for the last 
phase of the Battle of Britain had clearly been 
won. The course of the war, even before Pearl 
Harbor precipitated us into the struggle, indi- 
cated that some of the other functions of radar, 
particularly ASV, were to become extremely 
important. 

3 4 PROJECT II: FIRE CONTROL AND 
AUTOMATIC TRACKING-SCR-584 

The development of gunlaying radar at MIT- 
RL was much less influenced by British require- 
ments and British specifications than had been 
the case with AI. This was in part because the 
British Technical Mission had entrusted the 
problem of a microwave antiaircraft set, along 
lines already being followed in Britain, primarily 
to the National Research Council in Ottawa. At 
MIT-RL, therefore, the development proceeded 
along quite original lines. 

Antenna Scanning 

Objective 

Project II was not officially undertaken by a 
special group in the laboratory until January 
1941. It was decided that the microwave radar 
should be a precision system, using the novel 
principle of conical scanning to produce accu- 
rate pointing, and embodying the important fea- 
ture of wholly automatic tracking in azimuth 
and elevation. Once the system had picked up a 
target, for example an enemy aircraft, it was 
proposed to have it lock on and follow, the an- 
tenna continuing to point at the target despite 
high speeds or violent evasive action. Data on 
the plane’s three coordinates would be continu- 
ously fed to a gun or searchlight director. 

Theory of Operation 

Conical Scanning. In conical scanning the 
beam from the antenna is rotated at high speed 


44 


TECHNICAL PROGRAM OF THE RADIATION LABORATORY 


about the axis of a paraboloid, so that it describes 
a cone of revolution Avith its apex at the antenna. 
This produces the same effect as simultaneous 
lobe switching in the horizontal and vertical 
planes, that is, the rotating beam overlaps itself 
only at the axis of the paraboloid, and produces 
what is tantamount to a narrow pencil beam 
along the axis. The strongest signal is received 
from a target at which this pencil beam, and 
hence the axis of the paraboloid, is exactly point- 
ing. Conical scanning was first experimentally 
produced by wobbling the entire paraboloid, la- 
ter by spinning an eccentrically placed dipole. 
With the proper circuits, the angular deviation 
of the target from the axis of the parabolic re- 
flector can be detected and converted into an 
“error signal.’^ This in turn is converted by 
means of commutating circuits into a d-c voltage 
which drives the servomechanism and keeps the 
antenna pointing at the target. Before the ap- 
pearance of production equipment automatic 
tracking in range supplanted manual tracking. 

Range Measurements. To profit by the accu- 
racy in range measurement inherent in radar 
pulses, extremely precise range circuits were de- 
vised to produce special high-speed sweeps. A 
special range unit or synchronizer was built 
which produced sweep-generating voltages for 
the cathode-ray tubes, generated the trigger 
pulse to the driver unit of the modulator, and 
provided the range gates designed to eliminate 
target confusion, which is one of the principal 
obstacles to automatic tracking. For example, 
when two targets are at the same bearing and 
nearly the same slant range, the antenna may 
hunt between the targets or take up an inter- 
mediate position between them. Range gates are 
designed to remedy this difficulty by confining 
the reception of signals to a short interval of 
time, i.e., to a portion of the indicator trace. The 
so-called “Narrow Gate” first used in the experi- 
mental equipment, and the still narrow N“ Gate, 
were important features of MIT-RL fire-control 
radar. 

Experimental Systems 

A Project II roof system went into operation 
in February 1941 using what AI components 
could be borrowed from the higher priority AI 
program. Using a specially modified 30-in. para- 


boloid, a crude demonstration of conical scan- 
ning was possible by February 6. Although the 
most successful equipment to result from these 
early experiments was the mobile SCR-584, em- 
bodying all the features described in preceding 
text, the first efforts were directed toward using 
the conical scanning feature, without the addi- 
tion of automatic tracking, for an airborne radar 
gunsight and for a ship fire-control system. 

Airborne Gunlaying Radar. The aircraft gun- 
sight program, which was somewhat premature, 
never went beyond an experimental installation 
demonstrated at Wright Field in January 1942. 
The program of airborne gunlaying radar had to 
await the development of the lighthouse tube 
transmitter which permitted the design of com- 
pact lightweight systems. The U. S. Navy pro- 
gram resulted in what was chronologically the 
earliest (if not the most fruitful) production 
contract resulting from MIT-RL research and 
development. An experimental 10-cm gunlaying 
radar was tested at the Naval Proving Ground, 
Dahlgren, Virginia, during September and Octo- 
ber 1941. After a conference at the Bureau of 
Ships [BuShips] in January 1942, a contract was 
awarded to the Western Electric Company to 
build the Mark 9 radar based on the model that 
had been demonstrated. MIT-RL severed con- 
nections with the project at this point. Only a 
handful were ever built and none was ever in- 
stalled because the gun director for which they 
had been designed was cancelled. A similar fate 
was met by the Mark 10, a slightly improved 
Mark 9, though a few were installed on light crui- 
sers. Of the Mark 19 radar, a repackaged ver- 
sion of the Mark 10, about a hundred units were 
finally produced. Although later designs were 
greatly improved, microwave radar fire control, 
despite its potentialities, never became a main 
reliance of the fleet. 

Aircraft Scanning and Automatic Tracking. 
The delivery by GE late in May 1941 of an am- 
plidyne-controlled aircraft machine-gun turret 
on which a paraboloid could be mounted, made 
possible the first demonstration of automatic 
tracking in elevation and azimuth. This success 
led the laboratory to build a mobile, truck- 
mounted unit, the XT-1, to serve as an experi- 
mental system for further research. The system 
had both conical scanning and automatic track- 


MICROWAVE RADAR OVER WATER SG, SCR.582, ASG 


45 


ing. It was not originally intended that the XT-1 
should become a model for a specific military 
weapon, and work was undertaken in July 1941 
without specific Service request. The system was, 
however, demonstrated to the Signal Corps in 
December ; and in February 1942 it was tested 
by the Coast Artillery Board, where it displayed 
its ability to locate objects within less than a mil 
(1 mil = 0.06°) in azimuth and elevation and 
within 20 yd in range. This performance to- 
gether with its capabilities in automatic follow- 
ing, led the Antiaircraft Artillery Board to con- 
clude that XT-1 was superior to any equipment 
yet tested for the purpose of furnishing present 
position data to an antiaircraft director. As a 
result of these tests it was proposed to design a 
microwave and antiaircraft radar to be based on 
the XT-1. It was to be equipped to feed data to 
the M-4, M-7, and M-9 Army directors which in 
turn would be coupled to 90-mm power-driven 
antiaircraft guns. It was decided also to incor- 
porate a PPI so that the set could do its own 
searching, and dispense with an associated 
search radar to put it on the target. In April 1942 
the Signal Corps placed an order with GE for 
628 units of the SCR-584. Later this number was 
increased to nearly 2,000 and the production 
divided between GE and Westinghouse. This 
order was subsequently reduced by the Signal 
Corps. 

The SCR-584 differs little from the prototype 
in fundamentals. The numerous improvements 
were almost entirely of an engineering nature, 
carried out by GE engineers in consultation with 
MIT-RL. 

Application of SCR-584 

Experimental Use. The XT-1 not only served 
its purpose as prototype and testing unit during 
the entire design stage of the production of the 
SCR-584, but it was employed, with a success 
that surprised even its designers, as an experi- 
mental instrument for the careful tracking of 
high-speed targets. It was used successfully to 
determine the performance of new airplanes in 
high-speed dive tests, when for physiological 
reasons human pilots could not fly the plane and 
record the results, and when airborne recording 
instruments were unreliable. It was found able 
to determine the muzzle velocity of shells and the 


trajectories of shells or bombs. With the addi- 
tion of special recording equipment, the XT-1 
proved of great value in tracking aircraft dur- 
ing experimental and training bombing flights. 
The technique involved here was later adopted 
in the operationally important technique of 
close-support bombing. 

Field Application. The first production SCR- 
584 was delivered on July 15, 1943. Out of a total 
of about 1,600 sets supplied to the Army, about 
1,400 had been delivered by June 1944. The set 
made its operational debut on the Anzio Beach- 
head where its accuracy in shooting down Ger- 
man bombers, and its relative invulnerability to 
the jamming which had virtually silenced the 
SCR-268’s, contributed to the successful landing 
of supplies and the expansion of the beachhead. 
In the defense of the London area against the 
post-invasion onslaught of the V-1 flying bombs, 
the SCR-584 was used with spectacular success 
in conjunction with two other signally important 
weapons, the proximity fuze and the M-9 gun 
director developed by BTL. On the Continent, the 
SCR-584 was an important element of the de- 
fense of the Antwerp region, and was used in a 
new role, in conjunction with the MEW, in con- 
trolling and directing tactical air support of the 
ground troops. Although introduced more slowly 
into the Pacific Theater, it had already been in a 
number of important actions and was defending 
important supply bases at the time war ended. 

Another fire-control development, the Mark 
35 radar and its partner, the Mark 56 director, 
did not see action in World War II, but will be 
mentioned in Chapter 7 because it is a natural 
evolution of the automatic tracking developed in 
SCR-584. 

3.5 MICROWAVE RADAR OVER WATER 
SG, SCR.582, ASG 

The discovery in March 1941 that microwave 
radar performed admirably over water, led the 
laboratory to explore more thoroughly this be- 
havior of microwaves and to design sets to utilize 
it. In the spring, the roof group expanded its 
activities to become a systems group for the de- 
velopment of types of radar not in the province 
of Projects I, II, or III. This group of physicists 
and engineers built the first microwave ship- 


46 


TECHNICAL PROGRAM OF THE RADIATION LABORATORY 


board equipment, the first ASV systems and the 
first microwave system for coast defense and 
harbor-entrance control duties. These systems 
were all characterized by being relatively 
straightforward adaptations of the AI-10 sys- 
tems, with the incorporation of the PPI as the 
only significant innovation. 

Shipborne Systems 
Preliminary Tests 

In April 1941, the U. S. Navy granted permis- 
sion to the laboratory to install an experimental 
ship-search system aboard the USS Semmes, a 
“four-stacker” destroyer of World War I type, 
operating out of New London, Connecticut, un- 
der Lt. Comdr. (now Capt.) W. L. Pryor, Jr., 
and assigned to radio and underwater-sound ex- 
perimental work. Installation of the microwave 
equipment aboard ship began on May 6, and the 
first signals were obtained a week later with an 
A-scope. The first PPI signals were obtained 
aboard the Semmes on June 5, 1941. Between 
June 9 and July 1 the ship made coastwise cruises 
which gave excellent opportunities for observ- 
ing the system at sea. Land signals were picked 
up at 19 miles and ships were followed to a dis- 
tance of about 7 miles. During the rest of the 
summer and the fall innumerable changes and 
improvements were made in this flexible experi- 
mental equipment. By November the system was 
giving 4 miles range on submarines, 8 miles on 
aircraft, and 26 miles on land. 

Development of SG Systems 

Navy Installations. In June 1941, the Navy 
placed its first microwave radar contract with 
the Raytheon Manufacturing Company to de- 
velop, with the assistance of MIT-RL, a ship- 
board microwave set based on the experience of 
the Semmes installation. In the development of 
this system the Raytheon Company, the Naval 
Research Laboratory, and Massachusetts Insti- 
tute of Technology Radiation Laboratory can all 
claim a share. The resulting system, the rugged 
SG, has been the microwave set most widely used 
in the fleet, where it was especially valuable for 
station-keeping, as a navigational aid, and for 
low coverage general warning. The first produc- 


tion unit, apparently the earliest production 
microwave equipment, was installed on the USS 
Augusta and shipped out on April 5, 1942. Over 
1,300 SG’s (including their improved versions, 
the SG-l’s and SG-a’s) have been produced. They 
have been installed on nearly all classes of ves- 
sels of the fleet: on battleships, carriers, heavy 
cruisers, light cruisers, and destroyers. 

Coastal and Harbor Installations. During the 
summer and fall of 1941 an experimental 10-cm 
system, closely resembling the system aboard the 
Semmes, was installed in a truck to study the 
possible use of this type of equipment for harbor 
control purposes and coast defense. On Novem- 
ber 18, it was set up on Deer Island, a small pen- 
insula commanding the principal channel into 
Boston Harbor and the site of a harbor-entrance 
control post jointly operated by the Army and 
Navy. So successful was the equipment in aid- 
ing the work of the control post, by supplying 
accurate range and bearing on all ships entering 
or leaving the harbor, that after Pearl Harbor 
this experimental laboratory equipment re- 
mained on 24-hour duty until replaced by pro- 
duction equipment. As a result of visits to the 
Deer Island installation by Army and Navy offi- 
cers during December of 1941, the Army ordered 
a crash production of 50 sets based on the RL 
truck system. The production of these sets was 
undertaken by the Research Construction Com- 
pany, Inc. [RCC], NDRC’s factory-sized model 
shop, which went into operation late in 1941. 
The first of these production sets, to which the 
Signal Corps assigned the designation of SCR- 
582, was installed in June 1942, at the Boston 
harbor entrance control post. Five of the original 
crash units accompanied the American forces in 
the North African invasion, and were the earli- 
est microwave ground equipment to see action. 
Late in 1942, two modified SCR-582’s, provided 
with a larger paraboloid and, in order to get 
greater range, a high-powered modulator were 
sent to the Panama Canal Zone to supplement, 
by their low coverage, the longer-wave early- 
warning network. 

^ ^ ASV Microwave Radar 

Preliminary Tests 

The possibilities of microwave ASV equip- 
ment had been mentioned many times in early 


MICROWAVE RADAR OVER WATER SG, SCR-582, ASG 


47 


discussions at MIT-RL. The first steps were ta- 
ken in the spring of 1941, shortly after the his- 
toric flight in the B-18 flying laboratory, when 
the roof group initiated the adaptation of AI 
equipment to ASV purposes. An experimental 
set was built and installed during the summer in 
the first of many aircraft which the Navy as- 
signed to the laboratory for experimental work. 
This was an X JO-3, a Lockheed transport which 
had been specially adapted to this new job by the 
Naval Aircraft Factory in Philadelphia by the 
addition of a plywood nose, and other changes. 
The first airborne PPI was built for this system. 
The system’s performance was carefully tested 
on a number of flights out of Boston and Phila- 
delphia. It improved so noticeably that on Sep- 
tember 26, in an attempt to test the ability of the 
system to work through the overcast, a ship was 
picked up from 8,000 feet at a distance of 40 
miles. The PPI operator guided the pilot until he 
could see the ship from 2,000 feet. 

In September BuShips authorized MIT-RL to 
carry out further tests on microwave ASV with 
a view to helping the BTL develop an ASV-10 
for the U. S. Navy. It was finally decided that a 
semioperational installation should be made in a 
Navy PRM-1, a twin-engine Martin flying-boat. 
A system was assembled during December and 
first flown on January 3, 1942, on a trip from 
Boston to Philadelphia. The installation was 
carefully tested on flights out of Norfolk and 
from bases in Florida during January and Feb- 
ruary. At Banana River, Florida, comparative 
tests were run against a British ASV. By May 
1942, the system had been operated a total of 156 
flying hours and was reported as capable of de- 
tecting cargo vessels at 45 miles and submarine 
conning towers at more than 15 miles. 

Although it had originally been intended that 
the XJO-3 and PBM-1 systems experience should 
find expression in the ASC, the ASV system 
which BTL were designing for the Navy, the in- 
fluence was actually felt more directly in a set 
designed during 1941-42 at the MIT-RL for the 
British and, independent of the BTL, for the 
U. S. Navy. 

Field Trials 

At the end of July 1941, a representative of the 
British Air Commission arrived at MIT-RL to 


explore the possibility of acquiring a small num- 
ber of microwave ASV sets for use by the Coastal 
Command. These were to be installed in Libera- 
tor bombers being supplied to Britain under 
lend-lease. Two specially modified Liberators, 
known as Dumbo I and Dumbo II, doubtless be- 
cause the bulbous radar dome beneath the nose 
enhanced the planes’ already elephantine ap*- 
pearance, were equipped with prototype units of 
microwave ASV during the winter of 1941-42. 
The Dumbo I equipment flew for the first time 
from the East Boston Airport on December 11, 
1941, the day Germany and Italy declared war 
on the United States. It was successfully demon- 
strated shortly thereafter to British and Amer- 
ican officers and was flown to the United King- 
dom in March 1942, where it underwent trials in 
Northern Ireland during April. The second Lib- 
erator was rapidly equipped and demonstrated 
at the end of April to the Secretary of War, Gen- 
eral Marshall, General Arnold, and other high 
ranking officers. These two systems served as 
prototypes for a crash program of 17 similar 
systems manufactured by the Research Con- 
struction Corporation, of which 14 were for the 
British. The first of these DMS-1000 sets was 
handed over to the British representative in 
August 1942 ; the remainder had been delivered 
by December 1942. 

By the time the British received their first 
production unit, MIT-RL’s ASV equipment had 
already seen Service use and drawn blood from 
the enemy. The story of the 10 B-18 ASV equip- 
ments hastily thrown together at U. S. Army re- 
quest early in 1942 is of great importance in the 
history of the laboratory. Their success gave the 
organization much-needed confidence and a sense 
of direct participation in the war and in large 
measure made up for the disappointing and in- 
conclusive end of the AI program. 

Bomber Experience 

At the conference between MIT-RL personnel 
and representatives of the Air Forces held at 
Wright Field shortly after the Pearl Harbor at- 
tack, one of the officers present urged that it 
would be extremely valuable if a number of B-18 
aircraft or some similar type could be equipped 
on a crash basis with ASV equipment for Pacific 
patrol work. It was agreed that for lack of air- 


48 


TECHNICAL PROGRAM OF THE RADIATION LABORATORY 


craft the laboratory AI program had slowed up 
beyond resuscitation and .that the components 
intended for the British Beaufighters could be 
used, with only slight changes, for this purpose. 

The RL-AI specialists were put on this new 
problem, while the Army Air Forces brought to- 
gether from various parts of the country, under 
the command of the late Col. William C. Dolan, 
ten somewhat shop-worn B-18 planes. The planes 
and their crews began to arrive at the East Bos- 
ton Airport in February 1942. Working at high 
speed, MIT-RL installed equipment during the 
winter in all ten planes, provided the necessary 
spares, and equipped a testing and repair truck 
to service the sets. 

As the installations neared completion, it was 
decided not to disperse the planes, but to assign 
all the crews, at least temporarily, to Langley 
Field, where the first planes had already re- 
turned, late in March, with their new microwave 
equipment. Even before all the planes had left 
Boston, the first operational successes were re- 
corded. On April 2, one of the ASV-equipped 
B-18’s, piloted by Colonel Dolan, and with two 
MIT-RL staff members in charge of the equip- 
ment, shared in the rescue of a Navy observa- 
tion plane that had been forced down fifty miles 
at sea near Boston. The floating plane was lo- 
cated by means of the B-18’s microwave radar 
equipment and a destroyer was guided to the 
rescue. 

From Langley Field the first B-18’s were al- 
ready acquiring operational experience against 
German submarines swarming off the East 
Coast. On April 1, 1942, a B-18 on its first night 
patrol, homed unsuccessfully on an enemy sub- 
marine, somewhat later picked up radar signals 
from a second submarine, which disappeared be- 
fore a run could be made, and finally picked up a 
third submarine at a range of 11 miles from an 
altitude of 300 feet, homed on it and sank it. 
Another kill was made on a flight from Langley 
Field on May 1. On May 22 five of the crews were 
ordered to Key West and five to Miami, where 
they operated until June 19, making one attack, 
the results of which were undetermined. 

In July 1942, the first sea-search-attack group 
[SSAG] was activated under Colonel Dolan's 
command. This unit, consisting at first only of 
the B-18 crews, was intended to serve as a de- 


velopment and training unit to try out new anti- 
submarine weapons and evolve a tactical doc- 
trine. Seven of the B-18's with their MIT-RL 
equipment (three planes had suffered opera- 
tional damage beyond possibility of repair) re- 
mained with the group until its inactivation in 
July 1943. 

Following the aggressive principle of the com- 
manding officer that the enemy submarines 
should be sought out where they were known to 
be operating, the group was sent on detached 
service on two important occasions. Between 
August 15 and August 23, these planes flew 24 
missions off Key West, and made 2 attacks, both 
believed successful. In the autumn they flew 86 
antisubmarine missions from Edinburgh Field, 
Trinidad, which resulted in 6 sighting and 3 
attacks, one of them a probable kill. 

At the time of its inactivation in July 1943, the 
First SSAG had completed a total of 1,189 satis- 
factory ASV missions (i.e., without radar fail- 
ure) ; of these 323 were made with MIT-RL 
equipment, the rest being with the SCR-517's 
and SCR-717's that this group was the earliest 
to test operationally. The laboratory hand-built 
equipment gave a higher percentage of satisfac- 
tory missions than the SCR-517's, the earliest 
microwave production equipment of this type. 

None of the experimental ASV systems de- 
scribed up to this point had more than an indi- 
rect effect upon the design of production micro- 
wave equipment. The story of the ASG, however, 
is that of a set designed by MIT-RL, engineered 
in cooperation with the Philco Corporation of 
Philadelphia, and produced at great speed and in 
large enough quantities to have exerted a notable 
effect on the war against the submarine. 

Development of Blimp Equipment 

A group at the United States Naval Air Sta- 
tion at Lakehurst, New Jersey, expressed an in- 
terest, during October 1941, in a radar system 
for installation in nonrigid airships. Consulta- 
tions with MIT-RL members resulted in the de- 
cision to make an experimental installation in a 
K-3 blimp, using MIT-RL experimental equip- 
ment recently removed from the XJO-3 airplane. 

When experience had shown this idea to be 
sound, a conference was held at Cambridge on 
February 17, 1942, with Lt. Comdr. L. V. Berk- 


PROJECT III: LONG-RANGE NAVIGATION (LORAN) 


49 


ner and Lt. Comdr. D. T. Ferrier representing 
the Navy, to decide on the proper features for a 
production set to be installed in blimps. The ASC 
was considered but dismissed as too heavy and 
too bulky, and because production figures were 
not promising. It was pointed out that the Strom- 
berg-Carlson Company was building a new, 
lightweight pulse modulator, based on the lat- 
est MIT-RL developments and that it was de- 
signed to meet Navy specifications for such com- 
ponents. A decision was reached to design a new 
10-cm set around this pulse modulator and to 
give the production contract to the Philco Com- 
pany which had already attracted the attention 
of the Navy by its speedy performance on earlier 
contracts. The set was to have a PPI, whereas 
the B-18 systems and the Western Electric sets, 
ASC and SCR-517, had B-scopes. 

Final engineering design was worked out in 
close cooperation with the Philco engineers dur- 
ing 1942. Philco turned out a preproduction set 
in July 1942. In this same month the Navy em- 
barked on a heavier-than-air ASG program. 
Philco's first production set appeared in late 
October 1942. By mid-December, 28 production 
sets had been installed in PBM-3C flying boats 
at the Naval Air Station at Norfolk, Va. By 
March 1944 Philco had delivered 4,141 sets. 
These were widely used by the Navy in blimps 
and patrol planes, by the British, and in smaller 
quantities by the Army. 

3 6 PROJECT III: 

LONG-RANGE NAVIGATION (LORAN) 

^ ® ^ Theory of Loran 

The need for a system of long-range naviga- 
tion for ships and aircraft had been among the 
original proposals made by the Armed Services 
to NDRC and was discussed, as previously men- 
tioned, during the earliest conversations with the 
British mission. Early in October 1940, A. L. 
Loomis formally proposed to the Microwave 
Committee that they adopt a scheme in which 
pulsed radio waves from fixed stations are used 
to produce a grid or network of hyperbolic lines 
from which a fix can be obtained by an aircraft 
or ship carrying a specially designed pulse re- 
ceiver. In a simplified case, if each of a pair of 


synchronized transmitting stations several hun- 
dred miles apart sends out simultaneous pulses, 
a receiver at any point on the perpendicular bi- 
sector of the line between the stations will re- 
ceive the pulses simultaneously. At all other 
points within range of the stations there will be 
a fixed difference or delay in the time of arrival 
of the pulses, the value of this time difference 
depending only upon the geographical position 
of the receiver. The locus of those points on the 
earth’s surface having a constant time delay is 
one of a series of confocal hyperbolic lines gen- 
erated by the pair of stations. The time differ- 
ence determined by a special pulse receiver-indi- 
cator can then yield a line of position. When the 
time delay from a second pair of stations is 
translated into a second line of position, the re- 
sult is an accurate navigational fix. 

^ ® ^ Development of Loran 

Loomis’ proposal was adopted by the Micro- 
wave Committee, and a coordination committee 
for Project III was set up to arrange for the pro- 
curement, field installation, and testing of suit- 
able equipment. A frequency of about 30 me per 
sec was chosen. A transmitter with peak power 
of 2,000 kw was specified ; but the exact pulse 
rates and methods of synchronization were not 
settled when the original equipment was ordered 
in December 1940. 

After the organization at MIT-RL the techni- 
cal responsibility was assigned to a special navi- 
gation group set up in January 1941 under the 
direction of Melville Eastham. During the spring 
of 1941, while awaiting the delivery of the Proj- 
ect III equipment, this group concentrated upon 
a technical reconsideration of all aspects of the 
proposed high-frequency system. This review 
resulted in the small-scale development during 
the summer of 1941 of a system using medium 
frequencies. The initial tests were so successful 
that the original high-frequency plan was aban- 
doned early in 1942. This new system became 
\^no^xY 2 islong -range navigation [LRN] and these 
letters were later expanded into the word Loran. 

The basic evolution of the Loran system was 
virtually completed by September 1941 when the 
present system of receiving and comparing the 
time of arrival of pulses was evolved. This highly 
precise time-measuring technique used precision 


50 


TECHNICAL PROGRAM OF THE RADIATION LABORATORY 


circuits similar to those of the radar range unit 
and a cathode-ray tube indicator with a double 
trace. The pulses of two stations appear on the 
separate traces, which are carefully marked off 
by electronic time markers. By superimposing 
the pulses the time-difference can be read di- 
rectly from the scale with an accuracy of about 

5 msec. 

Tests of Experimental Models 

Low-power field tests were run in December 
1941 and January 1942 from two shore stations 
located at Montauk Point, L. I., and Fenwick 
Island, Delaware. Observations were made from 
Bermuda. The unquestionable success of these 
trials led to the expedited production of new 
high-power (100 kw peak power) transmitters 
for a demonstration in June 1942, when a Navy 
blimp carried aloft an experimental airborne re- 
ceiver-indicator for the first full-scale test of this 
system of navigation. Shortly after, observa- 
tions were made over an extended period from a 
Coast Guard weather ship in mid-Atlantic. 

Field Applications 

Station Network Installations 

The success of these demonstrations aroused 
intense Army and Navy interest. Early in 1942 
arrangements were made for the Navy to under- 
write the production and early installation of a 
number of shore stations and shipboard receiver- 
indicators by the MIT-RL. The first 14 trans- 
mitter-timers were manufactured before the 
end of 1942 by MIT-RL and RCC. The first 8 
transmitters were produced in the same period, 

6 by the Harvey Radio Laboratories, and 2 by 
Canada’s Research Enterprises, Ltd. The Fada 
Radio and Electric Company of Long Island City, 
N. Y., produced the first 50-or-so shipboard re- 
ceiver-indicators. 

In anticipation of formal Service backing, ar- 
rangements had already been made with the 
Royal Canadian Navy for the erection of two 
stations on the coast of Nova Scotia under the 
direction of MIT-RL personnel. During the sum- 
mer of 1942 three more stations were sited in 
Newfoundland, Laborador, and Greenland, and 
every effort was made to get the entire seven- 
station system in regular operation before the 
winter. The four southernmost stations, linked 


together so as to provide three pairs, began regu- 
lar service on October 1, 1942. Unforeseen dif- 
ficulties kept the remaining stations from regu- 
lar operation until the following spring. By July 
1943 the chain was officially turned over to the 
U. S. Coast Guard and the Royal Canadian Navy. 
Subsequent installations during 1943 in the Aleu- 
tians and the northeastern Atlantic were han- 
dled entirely by the Coast Guard and the British 
Admiralty, respectively. The equipment for these 
so-called standard Loran installations was 
wholly, or in large part, of MIT-RL design. More- 
over, the critically important timer units for 
these installations were manufactured solely by 
RCC and MIT-RL. During the second half of 
1944, and in 1945, a very large area of the Pacific 
Ocean was covered by Coast Guard Loran instal- 
lations made under Navy auspices at the direc- 
tion of the Joint Chiefs of Staff. 

The group that accomplished these results 
was never very large. In July 1941, it was com- 
posed of 10 staff members and two technicians. 
Two years later it had reached its maximum size 
of 73 persons, including 39 staff members. From 
the first, the essential differences between the 
work of the navigation group and the radar work 
of the rest of MIT-RL was recognized by the 
Microwave Committee, which set up a subsection 
to coordinate the Loran activities. This later be- 
came Section 14.2 of NDRC and finally was dis- 
solved when the Services took over general super- 
vision of the project. While in existence, this 
subcommittee arranged for the complete segre- 
gation of Loran research and development, as 
well as purchasing, shipping and field station op- 
eration, from the rest of the laboratory. At the 
Navy’s request, special security measures were 
adopted. 

Special Installations and Applications 

Skywave Synchronization. During the spring 
of 1943, the navigation group worked out the 
idea of synchronizing a pair of Loran stations, 
not by the directly transmitted ground wave, but 
by means of the sky wave reflected at night from 
the E-layer of the ionosphere. This technique 
made possible the nighttime use of baseline dis- 
tances of 1,200 to 1,400 nautical miles, which 
meant greatly improved geometrical accuracy 
and the possibility of navigation over land as 


RADAR ON THREE CENTIMETERS 


51 


well as over the sea. In the summer of 1943, a 
system using this technique was proposed to the 
RAF and accepted by them pending a successful 
test in this country, for use in nighttime opera- 
tions deep in enemy territory. This full-scale field 
test was successfully completed late in 1943. In 
the early fall of 1944 the system was placed in 
full operation, giving reliable nighttime fixes 
over all of Central Europe and as far east as 
Warsaw. After several months of trial use on a 
relatively small scale, it was discovered that the 
system had a sufficiently small probable error to 
permit blind bombing with an accuracy that com- 
pared favorably with radar techniques. A total 
of about 22,000 bombing sorties were flown by 
the RAF using SS (sky wave synchronization) 
Loran. 

Navigational Aid m Pacific Theater. Toward 
the end of 1943, it was suggested that Loran 
might be used in the CBI Theater to provide a 
navigational aid for plane traffic over “The 
Hump.” Simplified lightweight timers and trans- 
mitters were hastily designed and built by MIT- 
RL, and tested in the mountains of southern Cali- 
fornia. A chain of three stations was put in op- 
eration, under the direction of one of the most 
experienced MIT-RL Loran engineers, in the 
Assam region of India late in 1944. A second trip- 
let went into regular operation in the Kunming 
area early in 1945. 

Low-Frequency Loran. At the close of the war 
MIT-RL was engaged in an important develop- 
ment described as low-frequency Loran. Early 
experiments had made it clear that longer ranges 
could be achieved by using lower radio frequen- 
cies than the 2-mc per sec band which had been 
assigned to wartime Loran for reasons of expe- 
diency. 

The first experiments were performed in the 
winter and spring of 1944 and by April 1945, 
with joint Army-Navy backing, a full-scale 
three-station low-frequency system was in oper- 
ation on the east coast of the United States 
using a radio frequency of 180 kc per sec. Equip- 
ment for eight permanent installations of this 
sort was in the process of crash procurement for 
the Army Air Forces at the time of the Japanese 
capitulation. The field tests indicated that low- 
frequency Loran can provide reliable twenty- 
four-hour service with ranges of about 1,500 


nautical miles in most areas of the world. The 
peacetime possibility of improved Loran in an 
age of global air transportation can scarcely be 
exaggerated. 

3 7 RADAR ON THREE CENTIMETERS 

^ ^ ^ Early Experimental Objectives 

From the very earliest days of the laboratory’s 
program, it was generally understood that a 
strong effort should be made to devise microwave 
radar on a wavelength even shorter than 10 cm. 
To conservatives in military procurement this 
must have seemed a doubtful enterprise. It was 
already presumptuous enough to try to develop 
10-cm equipment to supplant the longer- wave 
radar which was only just going into production. 
To expect equipment on still another unexplored 
wavelength to be ready in time to be of use was 
no less than audacious. The problem at MIT-RL 
was what wavelength to choose, for it was pos- 
sible either to attempt a radical improvement 
by going to a wavelength as short as a few milli- 
meters in length, or to stay closer to 10 cm in a 
region where techniques already being perfected 
could be readily adapted, by scaling-down and 
other modifications, to the new wavelength. The 
choice of 3 cm was a somewhat arbitrary com- 
promise. It was close enough to 10 cm to offer a 
fair chance of success in a reasonable length of 
time, yet the gain of more than threefold in reso- 
lution would be worth a very considerable engi- 
neering effort. 

Experimental and Preproduction 
Systems 

Deer Island Trials 

The emergence of the first successful 3-cm 
magnetrons from the Raytheon model shop in 
the early spring of 1941 made possible the crea- 
tion of an advanced development group at MIT- 
RL whose task was to build an experimental 
roof system. Such a system was in operation in 
the middle of May 1941, giving echoes from 
ground objects six miles away with a 12-ft 
paraboloid. It was followed soon after by a sim- 
ilar system installed in a truck. This was placed 
in operation at Deer Island in Boston Harbor 
shortly after the attack on Pearl Harbor, and 
operated side by side with the XT-3 (10-cm) 


52 


TECHNICAL PROGRAM OF THE RADIATION LABORATORY 


truck system for almost three months, demon- 
strating its superiority over the 10-cm system 
in obtaining much higher resolution of targets. 

AIA Fighter Plane System 

On May 21, 1941 a discussion took place be- 
tween E. G. Bowen of the British mission and 
L. A. DuBridge, the director of the laboratory, 
during which it was agreed that the success of 
the 3-cm development suggested an immediate 
application in an AI for single-seated fighters. 
Proposals were drawn up for this development. 
The AIA program only took definite form when, 
in September 1941, the Navy expressed its inter- 
est in a combined interception and gun-aiming 
radar for its carrier-based nightfighter version 
of the Vought-Sikorsky F4U-1 aircraft. The 
specifications called for a compact radar having 
a weight of not more than 250 pounds, an an- 
tenna system with negligible drag, an accuracy 
sufficient for blind gun-aiming, a useful search 
range of two miles at altitudes of 2,000 or more 
feet, and a minimum dependable range of 500 
feet. The laboratory representatives were con- 
vinced that a 3-cm AI with a specially designed 
scanner and indicator could be built to satisfy 
these requirements. At almost the same time the 
Navy was persuaded to sponsor a simultaneous 
development by a newly created high power 
group of the MIT-RL of a height-finding and 
general control set for aircraft carriers. This set, 
which became the SM, will be discussed below. 

Initially the MIT-RL was asked to build three 
systems, one experimental and two preproduc- 
tion versions of the AIA, while advising the 
Sperry Gyroscope Company in the design and 
construction of ten preproduction systems. The 
laboratory’s experimental system was completed 
and tested early in June 1942 and was delivered 
to Quonset, R. I., for pilot training late in the 
same month. The two preproduction systems 
were completed by late October. With the assist- 
ance of the laboratory, Sperry’s first preproduc- 
tion set was finished and tested in April 1943. By 
June 1943, the company had delivered its ten 
preproduction sets. In October 1944 Sperry com- 
pleted its production of 604 sets. 

AIA-1 Improved System (AN/APS-6) 

In April 1943, having virtually fulfilled its 
commitments on AIA, the laboratory turned its 


attention to the development of an improved 
3-cm AIA called the AIA-1. This set was to op- 
erate at an altitude of 30,000 or more feet and 
was to incorporate such important new develop- 
ments as a 3-cm magnetron with higher power 
perfected in the interim. But the prime impetus 
for the AIA-1 program came from the installa- 
tion difficulties encountered with the AIA. In 
both sets the scanner was placed in a wing 
nacelle, and in the earlier set this meant running 
lengths of waveguide through the airplane wings 
to carry the r-f energy from the magnetron to 
the paraboloid. The AIA-1 was made possible 
by the development at MIT-RL of an important 
device called a pulse transformer which ampli- 
fies pulses of energy without appreciable distor- 
tion. This, in turn, made it possible to eliminate 
the long waveguide by placing the magnetron 
immediately back of the paraboloid in a unit 
called the r-f head which also included the pulse 
transformer, the TR box, and other r-f com- 
ponents. This improvement had first been intro- 
duced in the parallel 3-cm ASV development, to 
be discussed shortly. 

The MIT-RL completed its own experimental 
system in September 1943 while assisting West- 
inghouse in the design and development of a pro- 
duction set. Westinghouse sent its first prepro- 
duction set to the laboratory for tests on Decem- 
ber 1, 1943. Five months later the company 
delivered its first production unit of AIA-1 to 
which was given the joint Army-Navy designa- 
tion of AN/APS-6. A total of 791 sets had been 
delivered to the Navy by Westinghouse by April 
1945. The AIA-1 proved to be a much sturdier 
and better designed set than its predecessor and 
was being used in increasing numbers in con- 
junction with the SM aboard carriers of the fleet 
as the war came to an end. 

ASV Radar Equipment 

Preliminary Investigation. In the autumn of 
1941, coincident with the inception of AIA, pre- 
liminary investigations of 3-cm ASV applica- 
tions were being made by MIT-RL at the request 
of the Navy. As early as November 1941 com- 
ponents were being assembled at the laboratory 
for installation in a Navy JRB aircraft, a two- 
motored general utility transport, assigned to 
the use of the laboratory at the East Boston Air- 
port. This set, wholly experimental and not de- 


RADAR ON THREE CENTIMETERS 


53 


signed as a prototype of any development, was 
completed and flight tested in June 1942. Much 
flying was done during 1942 and 1943 to explore 
the behavior of the new frequency. The PPI 
photographs made from the air with this first 
higher-resolution microwave radar showed at 
once the great superiority of the new equipment. 
The greater detail and fidelity with which the 
3-cm image reproduced the natural features 
below the plane caused great excitement among 
those in the laboratory and in the Armed Serv- 
ices who were following this development. 

Torpedo Bomber (ASD) Radar Development. 
Meanwhile the Navy had been discussing with 
the laboratory the advisability of developing a 
3-cm production ASV equipment. In a report 
dated February 6, 1942, the laboratory formally 
submitted its proposal for a 3-cm equipment, 
the ASD, for installation in the Grumman TBF. 
The radar would be designed to furnish the pilots 
of torpedo bombers with information as to the 
position of surface vessels, especially at night 
or during overcast conditions. 

The Navy contracted with the Sperry Gyro- 
scope Company to develop a prototype (XASD) 
and to manufacture production sets based on 
that prototype. The laboratory accepted the 
somewhat vaguely defined position of adviser to 
Sperry during this development. 

Initially the XASD set used a 10-kw mag- 
netron, the output of which, as in the AIA, had 
to be fed through a long length of waveguide to 
an antenna assembly in a nacelle on the wing 
of the airplane. After considerable difficulty and 
many delays, largely inherent in the difficulty of 
this design, the XASD was installed and suc- 
cessfully test-flown in a Grumman TBF at the 
end of June 1942. With help from the laboratory, 
Sperry completed its experimental preproduc- 
tion set in July 1942. Ground tests were finished 
in August and Sperry began production imme- 
diately. Although the ground and flight tests of 
the XASD and of the preproduction set had been 
successful, the first production sets were not 
satisfactory. Dissatisfaction with them had two 
results ; first, research was started in the fall of 
1942 on a new and improved set to be known as 
the ASD-1 ; and, second, the production model 
of ASD was considerably modified and improved. 
Originally planned for the TBF plane, the ASD 


sets were diverted for installation by the Navy 
in PV-1 aircraft (Vega Ventura patrol bomb- 
ers). By June 1943, 600 ASD production sets 
had been delivered to the Navy; by April 1944 
the complete order of 3,400 sets had been com- 
pleted. 

Patrol Bomber (ASD-1) Radar Development. 
In a conference at MIT-RL on November 25, 
1942, the Navy and the laboratory initiated the 
ASD-1 program with the Philco Corporation as 
manufacturer. The essential differences between 
ASD and ASD-1 were to be an improved an- 
tenna, a more stable and accurate indicator, a 
40-kw magnetron, and the addition of a specially 
designed r-f head, based on the recently devel- 
oped pulse transformer. As in the AIA-1, this 
eliminated the long waveguide through the wing 
to the antenna in the wing nacelle. Although 
designed for the Grumman TBF and the Vought- 
Sikorsky TBU it was specified that the ASD-1 
should be adaptable to the PV-1 airplane. 

^ Development and Production 

of AN/APS-S 

MIT-RL was made a consultant to the Navy 
in the Philco contract, instead of an adviser, a 
decision which reflected an important change in 
the laboratory's relations with the manufac- 
turers. The responsibilities of the laboratory 
during the development and production stages 
of a project had up to this time not been clearly 
defined. In certain instances progress had been 
severely impeded because differences of engi- 
neering opinion arose between MIT-RL person- 
nel and the manufacturer which could not be 
resolved by any final arbiter. This fact became 
increasingly critical as it became more and more 
evident that the laboratory could not abandon a 
project at the experimental or breadboard stage 
as had been the tendency at first, but must fol- 
low it through development and production and 
even into field use. Experience had shown that a 
sterilizing deadlock was more liable to ensue 
when the laboratory cooperated with the larger 
concerns having imaginative and forceful re- 
search groups. Their long-established engineer- 
ing departments with traditional ways of doing 
things did not always take kindly to proposals 
from a newcomer. It was at about this time that 
the laboratory evolved a policy of working to a 


54 


TECHNICAL PROGRAM OF THE RADIATION LABORATORY 


large extent with smaller electronic concerns, or 
at least with companies having modest research 
and development organizations. MIT-RL be- 
came the design and development organization 
for a group of companies the production facili- 
ties of which were thereby brought in to relieve 
the already crowded schedules of the four large 
electrical concerns which the Army and Navy 
had been in the habit of entrusting with its con- 
tracts. Late in 1942, the notion of consultant 
status was evolved in conversations between the 
U. S. Navj^ and the MIT-RL to provide a formula 
by which the laboratory could continue active 
participation in the development of equipment 
as it went into production. 

In January 1943 Philco sent three engineers 
to the laboratory to work on a prototype. This 
was another new departure and an effective one. 
Where the laboratory had previously sent its en- 
gineers to advise a manufacturer at his plant, 
Philco reversed the procedure. With the appro- 


val of the Philco management, which agreed that 
two research organizations would only impede 
one another’s activity, MIT-RL served as the de- 
velopment group working directly with Philco 
production engineers, almost as part of the 
Philco organization. Philco’s own small but able 
research group was thereby freed to work on 
other problems. The Philco engineers completed 
their prototype at MIT-RL and shipped it to 
their factory. Concurrently the laboratory built 
an experimental XASD-1 set which underwent 
ground tests at the East Boston Airport during 
March, and flight tests during June 1943. In 
July, the first set built at the Philco factory was 
installed in a PBN patrol bomber by the Navy 
and tested at Anacostia. Its performance was 
comparable with that of the laboratory set. By 
the end of August, Philco had delivered nine sets, 
called the AN/APS-3, to theNavy. Sixteen months 
later that company’s remarkable production line 
had produced a total of 4,924 AN/APS-3 sets. 


Chapter 4 


THE COLUMBIA RADIATION LABORATORY 


4.1 FOUNDATION OF THE TUBE AND 
CIRCUIT LABORATORY 

B y the spring of 1942 the Massachusetts 
Institute of Technology Radiation Labora- 
tory [MIT-RL] found itself heavily involved in 
an expanding 10-cm radar program and at the 
same time deeply committed to 3-cm airborne 
development based on the 3-cm magnetron de- 
veloped there under the direction of 1. I. Rabi. 
Rabi had divided his original group, soon after 
the attainment of this early objective, into two 
parts: a magnetron group under G. B. Collins 
entrusted with carrying on an important pro- 
gram of testing and improving the 3-cm and 
10-cm magnetrons; and an advanced develop- 
ment group whose job it was to develop 3-cm 
components for operating systems and success- 
ful airborne equipment. 

One-Centimeter Magnetron Project 
Available Data 

It was at this time that it seemed propitious to 
consider opening up still another band and to 
undertake the development of a magnetron to 
operate in the neighborhood of 1 cm. Experi- 
mental magnetrons at this wavelength had been 
made before. The magnetron group at MIT-RL 
had operated a tube of this wavelength in Sep- 
tember 1941, using a 1-cm anode made for them 
in the Raytheon tube shop. This tube was oper- 
ated on the vacuum pump. Somewhat later one 
or more sealed-oif tubes were built by F. Hutch- 
inson of that group, but they performed very 
poorly. The British, too, had been working on 
this problem for some time with somewhat more 
continuity of effort. B. V. Rollin of Oxford’s 
Clarendon Laboratory reported in October 1941 
on the successful design of a tube operating near 
1 cm which gave 50 to 100 w of peak-power out- 
put. 

Organization Problems 
The fact that the magnetron group at MIT 
was already overburdened, as well as a number 
of related reasons, appeared to dictate the re- 


cruiting of a new team to handle the problem. 
This meant placing it outside the bustle of the 
swiftly expanding laboratory where the empha- 
sis was increasingly on systems development. 

Rabi suggested Columbia University. This 
suggestion, while a natural one for a member of 
its faculty to consider, had several special advan- 
tages. Columbia was sufficiently remote from 
the MIT-RL while permitting ready access to it 
whenever necessary; its situation permitted 
easy and immediate contact with BTL and with 
other important industrial concerns; and, as 
Rabi was doubtless aware, space could readily be 
made available. Perhaps centrally important was 
the fact that a New York location made it possi- 
ble to bring into the radar program several 
highly esteemed workers with whom Rabi had 
been earlier intimately associated and whose 
personal situation made it difficult for them to 
leave the city. 

Rabi put his suggestion before his New York 
colleagues late in February at an informal meet- 
ing attended by J. M. B. Kellogg, a younger col- 
league of Rabi’s in the Columbia Physics Depart- 
ment ; Polycarp Kusch, who until a year before 
had also been a member of the Columbia Physics 
faculty, but was then working for Westing- 
house ; and S. Millman, instructor in physics at 
Queens College. 

Approval of Extended Facilities 

On February 20 the suggestion for the opera- 
tion of a laboratory at Columbia University was 
brought before the Microwave Committee which 
was meeting in Washington. The committee rec- 
ommended that the NDRC consider the proposal 
for a tube and circuits laboratory and a contract 
with Columbia University for $140,000. It was 
specified that this laboratory would confine itself 
to developing components, and that MIT-RL 
would take over the development of all systems 
based on Columbia University components. Act- 
ing on the recommendation of the Microwave 
Committee, the NDRC passed on the proposal at 
its meeting of March 6, and in turn recommended 
that OSRD proceed with a contract. W’^hen this. 


55 


56 


THE COLUMBIA RADIATION LABORATORY 


in turn, was approved by the Director of OSRD, 
Irvin Stewart wrote to Columbia giving the uni- 
versity an informal authorization to proceed. 

Meanwhile preparatory steps were already 
being taken. Rabi undertook to obtain the neces- 
sary releases for Kellogg, Kusch, and Millman 
from their various institutions. On March 5 he 
visited Columbia University and conferred with 
Kellogg and Pegram. Dean Pegram completed 
Kellogg’s release and after some negotiation 
Kusch was given a leave of absence from West- 
inghouse. 

4.1.2 Organization of Columbia Radiation 
Laboratory 

We may date the beginning of the Columbia 
Radiation Laboratory [CUDWR-RL] from 
Kusch’s arrival on March 9 to join Kellogg. To- 
gether they made preparations to occupy half of 
the twelfth floor of the Pupin Physics Labora- 
tory, space that had housed the elementary phy- 
sics laboratories and which was being made 
ready for their use. Rabi authorized Kellogg to 
act in his name in all matters pertaining to pur- 
chasing equipment, hiring non-staff employees 
and making general arrangements. The first and 
biggest job was to purchase, or otherwise ac- 
quire, the necessary equipment for the labora- 
tories and the machine shop. Equipment was 
borrowed or purchased from the stock room of 
the Columbia University Department of Physics ; 
other items were borrowed from MIT-RL, 
bought in the open market, or bought upon re- 
lease by the MIT-RL’s own suppliers. On March 
30 Kusch was able to announce that their safe 
had arrived and, since they were now in position 
to handle classified material, he hoped that cer- 
tain fundamental papers that he listed would be 
sent to them. Since no self-respecting war re- 
search laboratory could exist without a safe, per- 
haps this is a preferable event from which to 
date the laboratory’s beginnings. 

Kusch and Kellogg made brief visits of a few 
days each to MIT-RL in Cambridge (Kusch late 
in February and Kellogg early in March) . Mill- 
man joined CUDWR-RL on March 26 and began 
a month’s stay at MIT-RL on that date. 

By the end of June CUDWR-RL consisted of 
the three staff members already mentioned 
(Kellogg, Kusch, and Millman) and of Arnold 


Nordsieck of Columbia University, who had also 
joined the laboratory. During the course of the 
summer CUDWR-RL grew with the addition of 
two more staff members : Simon Sonkin of City 
College and A. V. Hollenberg. 

A contract was entered into between OSRD 
and RCA for a tube shop for the Columbia Radia- 
tion Laboratory to be set up in that company’s 
Harrison, N. J., plant. Kusch wrote to Rabi on 
June 2 : ‘‘The present plan is for us to make cer- 
tain tubes for lab tests on the premises and to 
make parts for tubes which may be completed at 
RCA.” The shop was located in a special room of 
the Harrison plant and employed five people. 

To carry out its part of the project (or as it 
turned out, to do a great deal more than that, for 
CUWDR-RL soon turned into a small magnetron 
factory) it was of course necessary to set up a 
well-equipped machine shop. Some of the initial 
difficulties in procurement were overcome when 
it was possible to borrow a 12-in. lathe and a pre- 
cision bench milling machine from Hunter Col- 
lege, and a precision bench lathe and a sensitive 
drilling machine from City College. By the fall 
of 1942 the group had a fairly flourishing ma- 
chine shop, and in addition a glass-blowing 
room, and facilities for gold and silver soldering 
in hydrogen, and for the manufacture of cath- 
odes. The laboratory was already occupying all 
of the floor allotted to it. Besides its staff mem- 
bers, it now numbered four machinists, four 
technicians, four guards, two secretaries, two 
draftsmen, and a glass blower. The group re- 
mained small, in accordance with the original 
philosophy that attended its birth, despite a 
steady expansion which made the single floor the 
laboratory occupied singularly inadequate as far 
as space requirements were concerned. By April 
1944, 74 people were employed at CUDWR-RL 
and of these only 25 were full-fledged staff mem- 
bers. I. I. Rabi, as a nonresident director, con- 
cerned himself less with detail than with matters 
of policy. He gave his subordinates unswerving 
support and his advice in a number of critical 
junctures determined the direction of the labora- 
tory’s activities. With the single exception of the 
associate director, Kellogg, the men at Columbia 
kept close to the actual laboratory benches, them- 
selves conducting the work or directing it at 
close range. 


TECHNICAL DEVELOPMENTS: MAGNETRONS ON 1 CENTIMETER 


57 


4.2 TECHNICAL DEVELOPMENTS: 

MAGNETRONS ON 1 CENTIMETER 

Basic Research 

The work at Columbia went forward in close 
cooperation with MIT-RL, but with little or no 
attention paid to the parallel development taking 
place in England. There was, by contrast, close 
contact with BTL in all phases of the work and 
some exchanges with the General Electric Com- 
pany [GE]. 

At BTL, J. B. Fisk had made some strapped 
1-cm magnetrons that gave about 4-kw output. 
But attention at BTL shifted, in the summer and 
fall of 1942, to the development of the 725 3-cm 
magnetron. Nordsieck, of the CUDWR-RL, was 
borrowed by BTL to help in this work. Later Bell 
re-entered the 1-cm magnetron program with 
great vigor. 

Development of Design and Specifications 
Initial Experiments 

By the end of June 1942 the first four experi- 
mental 1-cm magnetrons were built and under- 
going tests. They were unstrapped tubes (since 
at that time strapping these tubes seemed to 
offer insuperable obstacles) of the vane and sec- 
tor type, made by soldering the vanes into a cop- 
per anode ring. These tubes gave radiation be- 
tween 0.97 and 1.0 cm, had an extremely short 
life of about six hours, and an almost negligible 
power output. Improvements were made during 
the summer and a meeting was held with repre- 
sentatives of MIT-RL, the Sperry Gyroscope 
Company, and BTL to decide on a value of wave- 
length in this range to be taken as a preliminary 
standard. The wavelength of 1.25 cm was chosen. 
The British later assented to this choice. 

M 4 Tubes 

By the fall of 1942 the Columbia group had 
turned out with their own facilities, and with 
some help from RCA's tube shop at Harrison, a 
number of so-called M 4 tubes. These were 14-slot 
vane and sector tubes that gave a wavelength of 
1.25 cm, had an efficiency of 10 to 12 per cent, 
and a peak-power output of about 7 kw. These 
tubes seemed to have a lifetime at least of the 
order of 20 hours. Most of the early samples 


were operated on the pump (several stations 
were available for this work), though some 
sealed-off tubes were made. A number of the lat- 
ter were sent to MIT-RL for testing. A series of 
experiments was undertaken to determine the 
proper size of cathode to use in these tubes. 

C-Tube and B-Tube Development 

In mid-autumn a tube of this sort, but with a 
specially designed cathode, was constructed and 
designated as the C tube. This showed enough 
promise to warrant building, during the winter 
of 1942-43, 50 of these tubes for careful testing. 
The C tube had a large cathode, the same 
size of that used in the 725, and the tube was 
operated with the same magnetic field strength 
as the 725. 

Modification of C Tube. In the spring of 1943 
the C-tube cathode was further modified as a re- 
sult of the rumor that Raytheon had found in the 
case of 3-cm tubes that putting shoulders on the 
cathode, of such a sort that they protrude into 
the anode cavity, produced tubes of extremely 
high efficiencies. At Columbia the name B tube 
was given to tubes modified to test this assump- 
tion. The addition of this added capacity in the 
tube did, in fact, produce tubes of higher effi- 
ciency than anything the Columbia group had 
attained up to that time : in the neighborhood of 
30 to 40 per cent. On the basis of what they now 
recognize to have been insufficient evidence they 
decided that these were the tubes to manufac- 
ture. But it soon appeared that the tubes were 
extremely short-lived and, as if this were not 
enough to disqualify them, suffered the addi- 
tional defect of moding badly. The B tube gave 
less than 50 hours’ service as compared to about 
300-400 for the C tube. 

Improvement of C Tube. Sylvania and West- 
inghouse had both been brought into the pro- 
gram as potential manufacturers of 1-cm tubes. 
Westinghouse soon showed itself somewhat 
less aggressive and successful and Sylvania 
emerged as the principal producer of 1-cm tubes. 
Sylvania delivered its first C tube on April 18, 
1943, and its second almost a month later. Shar- 
ing the excitement over the apparent superiority 
of the B tube, Sylvania undertook simultaneous 
work on both tubes. MIT-RL received its first 
B tube from Sylvania on August 23, 1943. 


58 


THE COLUMBIA RADIATION LABORATORY 


E-5-Tube Developments (3J30) 

The B and C tubes both had an output consist- 
ing of a pickup loop leading into a coaxial line. 
A waveguide output offered many advantages, 
especially that of making it easier to arrive at 
precise manufacturing specifications for the out- 
put, and making it more easily reproducible. 
Work was begun in the fall of 1942 on this prob- 
lem, but a successful solution was not apparent 
until the spring of 1943 when workers at Colum- 
bia were able to report that a waveguide output 
tube had been built which gave 19 kw peaks at 
20 per cent efficiency and 16 kw at 24 per cent. 
By the following autumn this E-5 tube was 
adopted as standard. 

Sylvania and Westinghouse were advised to 
drop their preparatory work on the C tubes and 
to concentrate on the E-5's. MIT-RL received its 
first Columbia E-5 in November 1943 and its 
first 3J30 (the production designation of the 
E-5) from Sylvania on December 17. While pro- 
duction was beginning at Sylvania some 40 E-5 
tubes were built and tested by the CUDWR-RL 
under the direction of S. Millman and A. V. 
Hollenberg. 

Modification of Designs and Methods 

Several important advances were made during 
the course of the E-5 development at Columbia 
and a number of different modifications in de- 
sign were tried out. One of these is the Package 
1-cm magnetron designed by Sonkin for use with 
lightweight permanent magnets. This has built- 
in iron pole faces and an axially supported cath- 
ode. From the standpoint of magnetron construc- 
tion, perhaps the greatest innovation was the 
process of “bobbing’’ the anode crowns. In the 
bobbing process the anode crown is stamped out 
in one motion by a sharp steel cutting instrument 
of complex shape. The bobbing process has been 
in use for a number of months and it is generally 
attributed by the Columbia group to GE. 

Shop and Testing Facilities 

CUDWR-RL was virtually its own model shop. 
It gave the casual visitor the impression of being 
composed mainly of machine shops. All the final 
assembly of magnetrons was done there, though 
many of the parts were made for them at the 
RCA Harrison plant. This rather reversed the 
original plan. A new model shop at RCA, Lan- 


caster, Pennsylvania, helped in the later stages. 
It was created by special NDRC contract, origi- 
nally to do work for the magnetron group at 
MIT, and began work early in 1944. 

Much of the space at CUDWR-RL was devoted 
to testing magnetrons. A battery of Raytheon 
service modulators and of high power link mod- 
ulators, both fundamentally of MIT-RL design, 
were clearly in evidence. The group at Columbia 
designed some of its own test equipment (such as 
a variable attenuator, a broad-band water load, 
and a new standing wave detector) and received 
useful suggestions from MIT-RL (as, for exam- 
ple, in the matter of the high-Q wavemeter that 
grew out of a suggestion of Zacharias) or used 
1-cm test equipment developed by MIT, such as 
1-cm spectrum analyzers of which two were sent 
from Cambridge. In a number of cases Rieke at 
MIT and Nordsieck of Columbia made develop- 
ments in parallel. 

4.2.3 Improved 1-cm Magnetrons 
Experimental Strapped-Tube Design 

At first blush it seemed improbable that the 
strapping technique used at longer wavelengths 
would be feasible at 1 cm. Sonkin and his co- 
workers, in May or June 1943, began the earliest 
Columbia attempts at making a strapped tube by 
the simple expedient of gouging away some of 
the anode to make room for the straps. They 
thought there would even be room for double 
strapping. The first of these 18-vane T tubes (Tl, 
No. 1) was completed on July 22. In these tubes 
the straps stood up above the top of the crown. 
The tubes were strapped differently from the 
3-cm tubes, because the pairs of straps are one 
above the other instead of side by side. The next 
step was to try a sharp vertical groove cut in the 
fins. These tubes, however, gave low power and 
low efficiency. The first good strapped tube was 
made in August 1943 and was of the type just 
described. This tube gave a peak power of 25 kw, 
an efficiency of 28.2 per cent, and a wavelength 
of 1.628. It was some time before a tube was 
made that could duplicate these results. All told 
about 15 experimental tubes were built using 
different types of strapping (with shorter rings, 
or with rings of somewhat different shape, or 
somewhat differently attached to the vanes) . 


TECHNICAL DEVELOPMENTS: MAGNETRONS ON 1 CENTIMETER 


59 


Radial Strapped-Tube Design 

About the beginning of 1944 radial strapping 
was adopted. Straps of this sort are easier to 
space and to inspect. A special jig was devised to 
facilitate assembly. Tubes of this series (the F 
or RF series as they were called at Columbia) 
gave efficiencies of nearly 30 per cent and power 
of the order of 50 kw. These tubes were double- 
strapped, and though the wavelengths (having 
been raised as is usually the case as a result of the 
strapping process) were still too high, it was 
hoped to bring the wavelengths down to 1.25 cm. 

The first anode blocks were made by casting a 
copper-gold alloy in a steel mold which was then 
dissolved away by acid. The later crowns (as 
they are called here) were done by the bobbing 
process. In order to prepare them to receive the 
straps the crowns were filled with Lucite and the 
concavities milled into the vanes. The Lucite was 
then dissolved out with chloroform. The straps 
were silver-plated and soldered to the vanes by 
heating in hydrogen. 

4.2.4 Rising Sun Magnetron (A Tube) 

The chief rival of the strapped 1-cm tube, and 
one of the most important developments of 
CUDWR-RL, is the tube which had been devel- 
oped to operate in the tt mode, yet without strap- 
ping. 

The original impulse leading to the develop- 
ment of this magnetron came from an inter- 
change of ideas between Nordsieck and Millman 
in the early spring of 1943. It was Nordsieck’s 
original suggestion that asymmetries might be 
introduced in the tube by means of bumps or 
grooves made in certain of the resonant cavities. 
By this means, if it could be found out how to do 
it successfully, it should be possible to imitate 
the effect of strapping. On rather intuitive con- 
siderations it was felt that if on a 12-vane or 15- 
vane tube the bumps or grooves were placed reg- 
ularly around the tube certain desired modes 
could be encouraged and others suppressed. A 
cold test was made on a 10-cm model of a 12-vane 
tube and it was proposed on April 7, 1943 that a 
15-vane tube be made. A 15-vane tube was first 
built, with grooves cut in every fifth sector. It 
was tested on April 12. Data were taken that en- 
abled them to plot curves of wavelength in centi- 
meters against the depth of the cut in inches. 


Tests were made on a 12- vane model. The results 
were very poor. 

It was then proposed to try the effects of a 
double slot, which would give further additional 
inductance. This was tried on a model of a 12- 
vane and then a 15-vane tube. In this case they 
got poor results, that is, poorer mode separation 
than with a single groove. 

At this point Nordsieck sat down and tried to 
make calculations on the basis of transmission 
line theory, computing the ratio of the wave- 
lengths for a cut and uncut cavity. He found that 
he could predict the results that had been ob- 
tained with the 16-vane tube. One afternoon at 
the end of June or early in July Nordsieck and 
Millman evolved the idea of cutting alternate 
cavities. Nordsieck then proceeded to work out 
the theory for this case, but they were so confi- 
dent that their idea was correct that they began 
experiments a day before the theory was fin- 
ished. They made a scaled-up model with 14 res- 
onators, every alternate one being cut. It was 
tested for the first time on the weekend of July 
11, 1943. 

On the strength of the cold test bench results 
they made a couple of tubes, but they were ex- 
tremely bad. Somewhat discouraged, they re- 
solved to put the matter on the shelf for a while. 
Later they got the apparently simple idea of cut- 
ting the grooves more deeply, which led to the 
final success. The tube that resulted has been 
called the Rising Sun or the A-tube. 

The race was now on between the Rising Sun 
and the strapped tube. The Navy placed an order 
with Western Electric for 10,000 1-cm tubes yet 
to be developed. A meeting was held on April 25, 
1944 and it was decided that BTL should begin 
work on the Rising Sun. 

4.2.5 Tunable 3-cm Magnetron 

The work of CUDWR-RL received a distinct 
impetus as a result of the decisions that were 
taken in the late spring of 1943 in the confer- 
ences held in London between the British and the 
members of the visiting United States special 
mission on radar. At the meetings of May 18 and 
May 19, 1943, between the Compton mission and 
the radar board working committee it was de- 
cided that the British should abandon all funda- 
mental work on 3-cm components to the United 


60 


THE COLUMBIA RADIATION LABORATORY 


States, but continue, in parallel with the United 
States, to do work on experimental 3-cm systems. 
America was to provide 3-cm magnetrons for the 
systems development work on both sides of the 
Atlantic. At the same time it was agreed that the 
development of tunable magnetrons, which the 
British were stressing in the hope that they 
would provide immunity to jamming, would be 
entirely entrusted to the United States. 

After the return of the Compton mission to 
this country in June, a number of conferences, 
formal and informal, were held involving mem- 
bers of the MIT-RL, the Armed Services, 
CUDWR-RL, and BTL. At one of these meetings 
held at MIT-RL it was agreed (since Rabi had 
sounded out the Columbia staff about it a few 
days before) that the BTL and CUWDR-RL 
should work closely together on the tunable 3-cm 
magnetron. Columbia then made plans to divide 
its staff, keeping part of it at its 1-cm work, but 
shifting another part to work on the problem of 
the tunable 3-cm tube. 

Available Data on Tunable Magnetrons 
At this time the tunable 10-cm magnetron, as 
contrasted to the tunable 3-cm, was well over a 
year old. The first tunable 10-cm, where tuning 
is effected by mechanical deformation of the 
magnetron cavity, is quite generally credited to 
Percy Spencer of the Raytheon Company. The 
earliest such magnetron brought to the attention 
of the MIT-RL magnetron group was one they 
saw in operation during the winter of 1941-42 in 
the Raytheon preproduction SG radar set at 
Deer Island, in Boston Harbor. Tubes of this sort 
were submitted by Raytheon and were tested by 
the MIT-RL during the spring and summer of 
1942. A number of the important mechanical 
features which have made the magnetron de- 
pendably operable, such for example as the idea 
of using ballbearings with a sylphon, were sug- 
gested by MIT-RL. 

Experimental Design 
Mechanical deformation of the sort used on 
3-cm did not appear feasible with the smaller 
magnetrons. Both CUDWR-RL and BTL experi- 
mented with tuning by means of plungers and 
pins inserted into the resonant cavities. BTL, 
largely under J. C. Slater’s inspiration, experi- 
mented with asymmetrical tuning of this sort. 


whereas Columbia, in the manner that will be 
shortly described, had great success with a sym- 
metrical design. The BTL group, which was de- 
signing a finished tube for production at West- 
ern Electric, agreed to adopt almost without 
change the electric features of the tube designed 
by P. Kusch of Columbia and known as the 
“Crown of Thorns.” 

Development of “Crown of Thorns” 

The Crown of Thorns was essentially a pack- 
aged 725 (a 3.3-cm tube of the hole and slot 
type) . Tuning was accomplished by inserting a 
set of metallic pins or plungers into all the reso- 
nant cavities. The possibility of tuning in this 
fashion was suggested at CUDWR-RL by Simon 
Sonkin, as a consequence of an earlier observa- 
tion. He had used small glass rods inserted in the 
magnetron cavities, during cold resonance tests 
of a 1-cm magnetron, in order to distinguish the 
magnetron resonances from resonances in the 
line. Sonkin put this idea into effect (although 
after its use by Kusch on 3-cm) in making a 1-cm 
tunable. He completed the first of these on July 
15, 1943. 

CUDWR-RL Experimental L2 Tubes 

Sonkin proposed a tuning structure with the 
structure supporting the pins between the mag- 
net pole pieces and the anode segments. It was 
Kusch’s suggestion in June 1943 that one could 
get a more efficient mechanical design and con- 
serve space by putting the supporting structure 
within the pole pieces. His first operating tube 
was completed July 10, 1943. This tube, which he 
called the LI, worked, although not well ; but it 
served to demonstrate the general validity of the 
scheme. 

Three tubes, called L2 tubes by the Columbia 
workers, demonstrated the possibility of using a 
short gap between the built-in pole pieces of the 
magnet. 

Kusch reported these results at a conference 
held at BTL in New York on August 17, 1943. 
At this meeting representatives of CUDWR-RL, 
BTL, Westinghouse and MIT-RL were all 
present. Kusch reported that his tube gave 
8 to 10 per cent tuning and an efficiency of 
about 45 per cent at the ends of the tuning 
range and 30 per cent at the dip in the 
curve. Fisk of BTL reported that his use of 


TECHNICAL DEVELOPMENTS: MAGNETRONS ON 1 CENTIMETER 


61 


a single plug in one resonant element gave 
roughly a 2.5 per cent tuning range over which 
the power remained roughly constant. The fre- 
quency shift was not linear with the displace- 
ment of the plug. The Columbia group expressed 
confidence that the minimum observable in their 
own tube could be removed. After some discus- 
sion it was agreed to push a tunable magnetron 
for the XL band, that from 3.53 to 3.33 cm, for 
this had first priority among the requests of the 
combined communications board. It was agreed 
at a later meeting to concentrate on the Colum- 
bia type of tuning device. 

Development of L-Series Tubes 

In consequence CUDWR-RL ordered special 
anodes from the BTL, slightly modified from the 
725A design, and intended for 3.5-cm tubes that 
would tune over the XL band. Since it was clear 
that the minimum in the power-wavelength 
curve resulted from the electrical properties of 
the magnetron end space, Kusch decided to 
change the resonant frequencies of the end space 
and, if possible, shift the minimum out beyond 
the tuning range. 

L3 Series. The first step was taken with a tube 
designated as the L3-3 tube, in which a simple 
ring was inserted in the end space to cut down its 
area and its inductance. In the next tube, L3-4, 
it was decided to extend this as a collar around 
the plunger. This tube was tested on September 
21, 1943, and was found to have a limited tuning 
range. The next two tubes, L3-5 and L3-6, were 
exactly like the previous ones except that the 
pins were larger, and consequently increased the 
tuning range, giving more megacycles per mil. 
These were tested on September 24 and Septem- 
ber 22 respectively; and it was found that, for 
the first time, tubes were at hand which could 
cover both the XL and XS bands, that is the re- 
gion from 3.13 to 3.53 cm. Kusch felt that, with 
these tubes, the problem was now well in hand. 
He and his co-workers accordingly made another 
25 tubes. 

LJf Series. The first series, L4, was intended 
for experimental use at MIT-RL. These were 
based on the 3.3-cm anode. Eight of these tubes 
were made, and of these five were satisfactory. 
They were designed between August 12-19, and 
the first tubes were tested in mid-October. They 


showed good tuning behavior, tuning over the 
range from 3.35 to 3.10 cm. 

L5 and L6 Series. A series of L5 tubes was 
designed and projected but never made. Tubes 
of a still different design made up the L6 series. 
The size of the end space was slightly altered to 
adapt the tube to another type of magnet ; and 
these tubes had 11 tuning pins in a 12-resonator 
tube, thereby demonstrating the possibility of 
reducing the number of pins without greatly dis- 
torting the tuning curve. Three of these tubes 
were made. At this point Kusch altered the shape 
of the collar, giving it a 45° angle at the wall in 
order to compensate for the increased capacity 
due to the greater size of the tuning pins. This 
improvement was introduced into tube L6-3, 
which was tested for the first time October 22, 
1943. 

L7 Series. Two tubes of the L7 type were 
made in which the gap length was reduced still 
further (from 0.400 in. to 0.370 in., the dimen- 
sion finally adopted) with consequent saving in 
magnet size. The tubes were both tested in mid- 
November 1943 and were found satisfactory. At 
this point in the development, during the design 
of the L7 tubes, BTL entered the picture and 
tried to make their first tubes. The first designs 
were not very satisfactory. Up to this point BTL 
had supplied the anodes and the 725A output cir- 
cuits and had been seeking to improve the latter. 

L8 Series. The L8 magnetrons were designed 
collaboratively by Kusch of Columbia and by the 
Bell engineers. The objective was to design a 
magnetron on sound mechanical principles that 
would be interchangeable mechanically and elec- 
trically with the 725. A decision had to be made 
as to whether it was to be a Rising Sun or a 
strapped magnetron. Although strapping would 
be a more conservative approach, it would mean 
an increase in mechanical difficulties. It was de- 
cided to use the Rising Sun design. Bell was as- 
signed the problem of developing a satisfactory 
magnet, subject to the limitation that it be inter- 
changeable with the magnet of the 725. BelFs 
first magnet design was much too large and cum- 
bersome and brought criticism on this score from 
both Rabi and Kellogg who went to Bell to regis- 
ter their disapproval. The Columbia workers 
then approached the Indiana Steel Company, 
which had made magnets successfully for MIT- 


62 


THE COLUMBIA RADIATION LABORATORY 


RL. This company brought forth a good design 
which was submitted to the Bell people. 

Final Design and Production 

On March 6, 1944, Fisk, Hagstrom, and Glass 
of Bell met Kusch and Nordsieck of CUDWR-RL 
at the Pupin laboratories and held a conference 
in which they thrashed out for the first time the 
elements of good mechanical design. On the basis 
of decisions made at this conference Bell went 
ahead with the design of the tube. The problem 
of production was turned over to the Chicago 
plant of Western Electric Company, but by the 
time the tube reached that stage the war was at 
an end. 

The other tube problem on which CUDWR-RL 


made a major contribution was the improved E-5. 
It had been a strapped magnetron. It was decided 
to convert it to a Rising Sun. This decision was 
made in sufficient time to allow for redesign and 
production by Sylvania. By war’s end several 
thousand tubes had been delivered by Sylvania. 

In its research in high-frequency tubes 
CUDWR-RL made one other contribution, this 
in the field of propagation studies during the last 
year of the war. CUDWR-RL determined experi- 
mentally the position of the water absorption 
band. To do this tubes were built which operated 
in the vicinity of 0.9 cm, and a magnetron was 
developed which would operate on a wavelength 
of 3.5 mm. 




Chapter 5 


SELECTED GROUND SYSTEMS PROJECTS 


5 1 HIGH-POWER RADAR FOR GROUND 
CONTROL OF INTERCEPTION, SCR-615 

I N THE SPRING of 1941, MIT-RL sent one of its 
section leaders, K. T. Bainbridge, to Great 
Britain to study the British radar development. 
He returned deeply impressed with the impor- 
tance of long-range early-warning systems, and 
especially with the lack of suitable height-finding 
provisions. In mid-September, a group was 
founded at MIT-RL under his direction to ex- 
plore the possibilities of high-power radar 
(which then meant radar handling any peak 
power well in excess of 100 kw) and to design 
a set with height-finding features to serve as a 
ground control of interception [GCI] and under 
certain conditions as a low-coverage general 
warning set. Stimulated by the needs of the AIA 
program, the group working on the problem of 
high-power radar devoted its attention first to 
developing a shipboard installation for carriers 
to be used in controlling AIA-equipped night 
fighters. 

5.1.1 Requirements of High-Power Radar 
It was hoped that magnetrons would be forth- 
coming on 10 cm that would give powers in the 
neighborhood of 500 kw. The use of high-power 
modulators and of large paraboloids, 6 to 10 ft 
in diameter, seemed to be the other principal 
requirements. Since coaxial transmission line 
would be subject to breakdown at these higher 
power levels, a 10-cm waveguide was designed 
along the lines that the advanced development 
section had worked out for 3 cm. 

Design Developments 
Experimental CXBL System 

An experimental roof system was put into 
operation in the first week of February 1942. 
During the next few months it was resolved to 
incorporate two important features : ( 1 ) conical 
scanning for precise positioning in elevation and 
azimuth, and (2) the instantaneous presentation 
of height. Since the height of the target is given 
by multiplying the slant range to a target by 


the sine of the elevation angle of the antenna, 
electric circuits were designed which performed 
this computation automatically so that height, 
corrected for the effect of the earth’s curvature, 
would be read directly and continuously on a 
meter. 

The roof system was successfully tested as a 
GCI system against the laboratory B-18 plane 
on May 15, 1942. In the spring of 1942 prelim- 
inary specifications for the shipboard set, the 
SM, were completed in conference with U. S. 
Navy representatives, and a letter of intent was 
given GE for manufacture of the equipment. 
Work was begun on a prototype, called the 
CXBL, to be produced at MIT-RL. Meanwhile 
in July an experimental system was set up at a 
field station on Beavertail Point, Jamestown, 
Rhode Island. Because of the proximity of the 
Naval Air Station at Quonset it was possible to 
test this new type of system against U. S. naval 
aircraft. The installation was also used to try 
out components and design features of the 
CXBL. The CXBL equipment was completed 
and installed before the end of March 1943 on 
CV-16, the USS Lexington. This experimental 
unit had extensive operational use in the Pacific 
before it was replaced by production equipment. 

Experimental SCR-615 Model 

The parallel development went forward to 
produce a GCI set for the Army designated 
SCR-615. An experimental prototype was sent 
to the Army Air Force School of Applied Tactics 
[AAFSAT], Orlando, Florida, where it was 
tested late in 1942. Another was installed at 
Panama, as part of the Caribbean defense sys- 
tem, early in 1943. Still another laboratory-built 
set was sent to England in the early spring of 
1943 where it was set up for testing at Worth 
Matravers. Prototypes were also delivered to 
Camp Evans Signal Laboratory, Belmar, New 
Jersey, and to the Westinghouse Electric and 
Manufacturing Company which was elected to 
produce the SCR-615. The production units be- 
gan to appear in the summer of 1943. About one 


63 


64 


SELECTED GROUND SYSTEMS PROJECTS 


hundred were produced in the next two years. 

The SCR-615 was not widely used or thor- 
oughly satisfactory as a GCI set, in fact it did 
not see extensive service even as a warning de- 
vice. The set was extremely complicated and 
difficult to maintain, though this was somewhat 
less true of later models. One unit was used by 
the British Admiralty at Dover Castle for early 
warning. Two sets in mobile form were sent to 
France, where at least one of them was used as 
a height-finding set with an MEW installation. 
Two sets served in Corsica, one at Cap Corse 
with an MEW which covered the invasion of 
southern France, another at Ajaccio where it 
was used as a CCI set and reportedly was suc- 
cessful in bringing down a JU-88. A few sets 
found their way to the Pacific. 

5.2 MICROWAVE EARLY WARNING 
[MEW], AN/CPS-1 

Early Developments 

As a high-power set for early warning, a func- 
tion for which it had not been primarily designed, 
the SCR-615 was soon outclassed by a now illus- 
trious set for microwave early warning [MEW], 
which has received the joint Army-Navy desig- 
nation of AN/CPS-1. MEW was an independent 
outgrowth of the same interest in high-power 
sets which had given birth to the SCR-615. In 
particular, the set was conceived during the 
months immediately following the Pearl Harbor 
attack when it appeared likely that a powerful 
early-warning system might well be needed to 
protect the West Coast against Japanese air 
assault or even invasion. 

Requirements of MEW 

A careful study was made of the conditions 
which such an early-warning device should sat- 
isfy in order to give adequate protection, due 
regard being paid to the speeds of attacking 
bombers and the rates of climb of defend- 
ing fighters. It was determined that the beam 
should reach an altitude of 40,000 ft at 200 miles. 
To produce this coverage it turned out that a 
fan beam 3 degrees wide in the vertical plane 
and extremely narrow in the horizontal plane 
was desirable; while the beam was narrow 
enough in the vertical plane to give low coverage 
its breadth enabled it to sweep the sky without 


recourse to complicated scanning. The high gain 
required in the horizontal plane in order to attain 
the desired range gave the set the incidental 
benefit of extremely high resolution. The MEW 
project took form at MIT-RL when in the spring 
of 1942 it was decided to produce the fan beam 
by means of a linear array antenna which was 
being simultaneously considered as a means of 
producing a high-gain antenna for bombing 
purposes. 

MEW Antenna. The first antenna planned for 
the MEW system was to be a so-called leaky pipe 
linear array in which a succession of holes cut 
in a waveguide served as the sources of radiation. 
This was soon replaced by a linear array con- 
sisting of a row of dipoles to which energy was 
fed by means of probes inserted into a length of 
waveguide. The use of probes allowed the pat- 
tern of radiation to be adjusted as required. The 
linear array was backed by a cylindrical para- 
bolic reflector. 

First MEW Installation. The first MEW sys- 
tem was assembled in the late summer of 1942 
and installed in a special structure, resembling 
a gigantic radome, raised above the second level 
of the penthouse of MIT-RL Building 6. The r-f 
parts of the equipment were mounted all to- 
gether back of the reflector, while the indicators, 
the power supply, and high power Link modu- 
lator were in a room underneath. The linear 
array was 16 ft long; the reflector, 16 ft long 
and 10 ft wide. 

5.2.2 Critical Development Problems 
Power Requirement Problems 

Many of the characteristic features of MEW 
resulted from the necessity of handling large 
amounts of power, for it was hoped that a system 
could be designed to give a megawatt (10® w) of 
pulse power. The “back-of-dish'^ design is a case 
in point, for it made it unnecessary to carry r-f 
power over long distances. Waveguide, which the 
earlier group working on high power had intro- 
duced for 10 cm, was even more important at 
the high power levels envisaged for MEW, for 
though coaxial line might have carried a few 
hundred kilowatts without arcing, waveguide 
could carry ten times that amount. The extremely 
high power levels gave rise to problems that had 
not been encountered, or at least not in such 


MICROWAVE EARLY WARNING 


65 


critical form, with low-power systems. Arcing 
of the magnetron input feed and serious crystal 
burnout were the most persistent problems. The 
latter was due to the unsuspected strength of one 
harmonic of the radiation frequency which 
leaked through the TR box and injured the crys- 
tal. The development of a special crystal mixer 
with a choke to eliminate this harmonic was a 
necessary and important step. 

Indicator Problems 

Flight Test Results. During the fall of 1942 
MEW was flight tested almost daily against U. S. 
Army and U. S. Navy aircraft flown from the 
East Boston Airport. It had not been clear at first 
what indicators would be required. These tests 
showed that the original indicators, planned 
before the MEW was actually put in operation, 
were inadequate to handle the unexpectedly 
large amount of information the set provided. 
As a result of these tests an indicator system 
was adopted that consisted of an A-scope, a 
B-scope, and two 7-in. PPFs with ranges out to 
200 miles. The flight testing also verified the 
theoretical shape of the beam and revealed the 
need for an auxiliary antenna to provide high- 
level coverage close to the station. It also resulted 
in altering the dimensions of the principal re- 
flector. 

Result of Increasing Installation Elevation. 
In the spring of 1943 a second MEW was set up 
on a 100-ft tower at a site on the Gulf Coast of 
Florida near Orlando. In this system the power 
output of the magnetron was more than doubled, 
which revived the problem of crystal burnout 
and required a careful redesign of the dipoles. 
The set was supplied with two 12-in. PPPs, one 
to handle the signals from the principal beam, 
the other for the auxiliary gap-filling beam ; and 
there were in addition three B scopes and a par- 
ticularly flexible precision indicator called a 
''micro-B.” The greater range resulting from the 
elevation of the installation, the higher output 
power, the longer array (i.e., with higher gain) 
caused the main beam to fill to capacity the indi- 
cators that had been intended for both beams. 

The extraordinary traffic handling capacity 
of the MEW made a great impression upon the 
Army officers at AAFSAT. Using existing radar 
equipment it had been customary to report all 


isolated information to AAFSAT filter center; 
but with the advent of the MEW, which on cer- 
tain days could have reported as many as 12,000 
plots, the filter center would have been jammed 
with information telephoned in from the MEW 
site. A system of “prefiltering'' the tracks, at the 
MEW site, that is, sending on only clearly de- 
fined tracks to the filter center, was evolved to 
avoid clogging the center. 

0.2.3 Practical Applications of 

Experimental Models 

Experimental Experience 

Under the supervision of Col. T. J. Cody, head 
of the Air Warning Department of AAFSAT 
and a member of the Air Forces Board, rigorous 
tests were carried out during the summer and fall 
of 1943 to test the potentialities of the system. 
The conclusions were uniformly favorable and 
Colonel Cody satisfactorily confirmed his own 
first impression that the Air Forces had “hit the 
jackpot." The new and extremely powerful radar 
was readily adapted to Air Forces, thinking 
which had already decisively shifted to the offen- 
sive ; at AAFSAT considerable thought was paid 
to the possible uses of MEW as a control instru- 
ment in aerial offensive warfare, and the result 
was a campaign, in which Cody was a ringleader, 
to have the MEW designed so that it could be 
made mobile. 

The manufacture of 100 MEW sets based on 
the MIT-RL prototype at Tarpon Springs, Flor- 
ida, was entrusted to GE in the early summer of 
1943. MIT-RL was to serve as consultant. At a 
conference held in General McClelland's office 
in the Pentagon in August 1943 it was agreed 
that the production sets would probably not be 
available before early 1945 and that operational 
experience with the equipment was urgently 
needed. The laboratory agreed to build a total of 
five MEW sets on a crash basis (this was later 
increased to seven) , one to go to England for the 
use of the Eighth Air Force, the rest to go to the 
Southwest Pacific, the Central Pacific, and the 
Aleutians for use in training. 

Field Operations 

Of the seven preproduction MEW's for over- 
seas use, only one finally was sent to the Pacific, 


66 


SELECTED GROUND SYSTEMS PROJECTS 


where it was installed on Mt. Tapolchau on 
Saipan in January 1945, and served both as a 
defensive warning system and to keep track of 
homecoming B-29 raiders. The crews of at least 
two downed B-29’s and one P-38 were rescued as 
a result of information from the MEW. 

British Experience. The second MEW’^ pro- 
duced, set up at Start Point, Devon, in January 
1944, was the first of the crash units to reach a 
theater of operation. The site was suggested by 
the British to complete a chain of Type 16 sta- 
tions they had set up at Dover, Ventnor, and 
Beachy Head. The Start Point station, serving 
both as a training station and an operation unit, 
was manned jointly by British and American 
personnel, and aided by a British Type 24 height- 
finder worked with Eleventh Fighter Group 
RAF in controlling offensive fighter sweeps 
against the Continent. 

It was here that the true power of MEW as an 
aircraft control center first was clearly demon- 
strated. Many changes in equipment and in mode 
of operation were made before the set could 
function as a self-contained control station. 
These innovations, among them the use of a 
vertical glass screen for plotting, and the use by 
the controllers of “off-center” PPFs (designed 
at BBRL) , were adopted for later sets. 

During the D-Day operations, the night of 
June 5-6, 1944, the Start Point MEW performed 
three types of supporting operations. The first 
and most continuous was maintaining a patrol 
of Thunderbolts flying off the Brest peninsula. 
A second job was sending fighter bombers over 
various targets. A third was aid in the rescue 
of pilots downed in the channel. The MEW con- 
trol room provided a grandstand seat for follow- 
ing the aerial assault upon the Normandy beach- 
head. Shortly after D-Day, this MEW, handed 
over to the 19th TAG, Ninth Air Force, was 
made mobile and was used with great success to 
track the V-1 flying bombs. Later it was sent to 
the Continent. 

Mediterranean Experience. In the meantime, 
the first crash model of MEW, which had re- 
mained in Florida for training purposes, was 
removed at the request of the Air Forces and 
taken to the Mediterranean Theater, where it was 
installed in May 1944 on a northernmost head- 
land of Cap Corse on the island of Corsica. This 


station remained in operation until the end of 
August, and afforded a view of the air activities 
of the invasion of southern France on August 15 
comparable to its companion in England on 
D-Day in Normandy. 

Mobile System in Continental Operations. The 
third MEW produced was made mobile directly 
upon arriving in England in the spring of 1944 
and crossed the Channel to France on D-Day 
plus 6. Located at a point called Greyfriars on 
the East Coast of England from June to October 
1944, the fifth MEW was assigned to the Eighth 
Air Force to follow bombing missions also, with 
the help of the height-finding Type 24, to ren- 
dezvous planes, control fighter escorts, and direct 
fighter sweeps against enemy airfields in advance 
of the bomber stream. In October, the Eighth Air 
Force decided that the set would be more useful 
nearer its targets. It was made mobile and 
shipped to Holland and assigned full responsi- 
bility for control of all Eighth Air Force fighter 
missions over the Continent. 

5 3 FIRE-CONTROL RADAR FOR SHORE 

BATTERIES, SCR-598 OR AN/MPG-I 

• 

Requirements and Characteristics 
Need for Radar in Coastal Defense 

In 1941 the Coast Artillery Board, after sev- 
eral years of study, found that the coast defenses 
of the United States against motor torpedo boat 
attack were inadequate. The development of 
the 90-mm gun Ml, of gun data computer T-13 
for the 90-mm gun, and of gun data computer M8 
for 6-in. and 8-in. harbor defense batteries were 
initiated. In May 1942, motor torpedo boat at- 
tacks on our harbors were considered a possi- 
bility and while there was an excellent general 
surveillance set, the SCR-682, there was no radar 
equipment to detect and track small and highly 
maneuverable craft. 

After conversations with MIT-RL representa- 
tives from May to July, Col. W. B. Bowen, Presi- 
dent of the Coast Artillery Board, in a letter to 
the Chief of Ground Requirements Section, on 
August 3, 1942, proposed military characteris- 
tics for a radar to replace SCR-296, designed for 
installation in the Battery Commander’s Station 
of an emplacement for 90-mm anti-motor torpedo 


FIRE-CONTROL RADAR FOR SHORE BATTERIES 


67 


boat guns. He also recommended that RL be re- 
quested to design and develop the radar unit, 
on September 2, 1942 the laboratory received the 
request for a pilot model designated SCR-598. 

The resulting system was the most effective 
fire-control radar for seacoast artillery in oper- 
ation at the end of the war and one of the most 
unique 3-cm systems to come out of MIT-RL re- 
search and development. 

The high accuracy of the guns to be controlled 
and the requirement of handling 70-knot boats 
at 500-yd range determined certain design fea- 
tures. A beam narrow in azimuth and with low 
side lobes and the use of a 0.25-msec pulse were 
necessary to give the resolution and angular 
discrimination required. 

Design Features of SCR-598 

Antenna and R-F System. The most original 
feature of SCR-598 is the antenna and r-f sys- 
tem. Optical mirror theory solved the antenna 
problem. For this reason the antenna is called a 
“Schwarzschild” since its geometry is derived 
from the Schwarzschild astronomical telescope. 
The radiator is a folded, sectoral horn. Sectors 
of the folded waveguide are equivalent to the 
diametrical sections of mirrors in the optical 
system which was used as a guide in design. In 
operation r-f energy is fed into a folded piece of 
waveguide from a horn which scans in the hori- 
zontal plane. A plane wave 0°.6 wide, swept 
through 10° in azimuth and sweeping 16 times 
per second, is produced. For search the scanning 
system is stopped and the entire antenna is ro- 
tated through 360°. The antenna assembly is 
housed in a plywood shell (called from its shape 
the “bathtub'') which is supported on a pedestal 
similar to the one used for SCR-584. 

hidicator Designs. Several indicators are pro- 
vided. For search there is a 7-in. PPI with two 
scales, 30,000 and 80,000 yd. For these, continu- 
ous or sector scan may be used. The 7-in. B scope 
presents an expanded version of a section of the 
PPI and covers an area 2,000 yd deep and 10° 
wide and may be centered anywhere within the 
tracking range of the set. A second B scope is 
provided for shell-spotting which makes it pos- 
sible to read range and azimuth deviations from 
the center of impact so that after correction 
future rounds may fall directly on the target. 


5.3.2 Development and Performance of 
AN/TBG-1 and AN/FPG-1 

The MIT-RL prototype was assembled in mo- 
bile form and after five days of testing around 
Boston Harbor it was shipped to Fort Story, 
Virginia, in November 1943. Firing tests which 
were spectacularly successful were carried out 
in the presence of U. S. Army and British ob- 
servers. The mean tracking error was found to 
be 5 yd in range and 0°.03 in azimuth. In convoys 
large ships such as carriers could be distin- 
guished from smaller craft such as destroyers 
and even PT boats. 

The Bendix Radio Division of Towson, Mary- 
land, had been called in to prepare for production 
and had sent engineers to the laboratory to fol- 
low the development in February 1943. At the 
end of the year, however, the military situation 
had changed to the offensive and it was thought 
no longer necessary to produce the fixed installa- 
tion. Therefore the SCR-598 became the trans- 
portable AN/TPG-1 for use with mobile seacoast 
artillery and at the request of the Marine Corps 
the mobile version AN/MPG-1 was ordered. The 
fixed version AN/FPG-1 was at first abandoned 
and later reactivated when it was planned to 
install the equipment at fixed harbor defense 
batteries in Hawaii, Panama, and Alaska. 

In the spring of 1944 MIT-RL agreed to send 
the prototype SCR-598 to the Pacific for tests 
at Oahu and to furnish personnel to install and 
operate it there. Extensive demonstrations were 
carried out with 90-mm, 155-mm, 12-in., and 
16-in. batteries. With a locally trained crew 
average tracking and spotting accuracies were 
found to be about 0°.05 in azimuth and 10 yd 
in range. Ships could be distinguished as sepa- 
rate targets when separated by only 50 yd. 
Splashes from 155-mm shells could be spotted at 
ranges out to 28,000 yd. 

After these tests SCR-598 was transported to 
Iwo Jima where it arrived on April 25, 1945. 
Some time was taken in arranging for a semi- 
permanent site so the set was not turned on until 
May 2, 1945. Although the AN/MPG-1 was in 
production and several sets had been shipped to 
the Pacific by V-J Day the MIT-RL set was the 
first and only one to see service in a combat area. 


68 


SELECTED GROUND SYSTEMS PROJECTS 


5 4 BEAVERTAIL HEIGHT-FINDER, 
AN/CPS.4 

Report of Ad Hoc Committee 

Early in 1943 E. L. Bowles, expert consultant 
to the Secretary of War, set up an ad hoc com- 
mittee, headed by J. A. Stratton of his office, to 
review and make recommendations regarding 
the then chaotic state of the U. S. Army ground 
radar program. The committee submitted its re- 
port in the summer of 1943 ; it was accepted by 
the U. S. Army and resulted in a sharp curtail- 
ment of its radar program. 

Development of AN/CPS-5 Equipment 

Nevertheless, the report encouraged the de- 
velopment of a 10-cm height-finding set to be 
used with the AN/CPS-5, a 1,200-cm search set. 
This became known in the laboratory, because of 
the shape of the beam it produced, as Beavertail. 
It was officially designated AN/CPS-4. The Sig- 
nal Corps asked the laboratory to be consultants 
on this development, with the Federal Radio and 
Telephone Corporation (at that time, the in- 
tended manufacturers of the equipment) acting 
as the designers. By December 1943, however. 
Federal had dropped from the picture, partly be- 
cause of the plant expansion which the company 
said was required to build 200 models, partly be- 
cause of the company’s unwillingness to guaran- 
tee delivery dates. GE, already the manufac- 
turer of the CPS-5 equipment, took over in early 
1944 and received a contract for 100 models, with 
MIT-RL as consultants. 

Antenna and Indicator Design 

It was chosen to design an antenna narrow 
enough in the vertical plane to permit direct 
reading of height from the angle of the antenna. 
The CPS-4 antenna was horn fed with a refiector 
20x5 ft shaped as an elliptical section of a para- 
boloid. The antenna gave a beam 1.2° wide in the 
vertical plane, and to pick up the targets in alti- 
tude this was raised and lowered 25 cycles per 
minute by nodding the antenna structure. This 
was a height-finding principle favored by th(^ 
British. Signals were displayed on a special indi- 
cator which plotted elevation angle against 
range (out to 90 miles) and cut out ground clut- 
ter except for the baseline of the scope. 


Test Performance 

In April 1944 a laboratory-built, experimental 
CPS-4 was set up at Bedford Airport to check 
general performance, height accuracies, and 
range. Height accuracy tests showed better than 
±1,000 ft at 60 miles. By May a final draft of 
specifications had been given to GE, and a pro- 
duction schedule had been set up which called 
for first deliveries in May 1945. In August, the 
Bedford model moved to Leesburg, Florida, for 
operational tests in conjunction with the V- 
beam equipment, under the direction of the Or- 
lando Army Air Forces Board. These tests indi- 
cated height errors of the order of ±300 ft. An 
average of 3.6 sec was required to fix the height 
of a target, once its range and azimuth had been 
obtained from the associated search set. 

The first production model CPS-4 came out in 
June 1945. Several CPS-4 sets were shipped to 
the Pacific during July and August, but none 
arrived in time for combat. 

5 5 V-BEAM, AN/CPS-6, RADAR FOR 

EARLY WARNING, ACCURATE HEIGHT- 
FINDING, AND TRAFFIC CONTROL 

Specifications and Characteristics 

On March 20, 1943, the steering committee of 
the laboratory approved a project suggested by 
the Army for a portable ground control of inter- 
ception [PGC] set to give wide coverage and 
great raid-handling capacity as well as rapid and 
accurate height-finding. According to the Army 
specifications, readings of height were to be sup- 
plied every 10 sec with an accuracy of 500 ft. 

After several months of canvassing the possi- 
bilities of separate search and height-finding 
systems, the laboratory began the design of a 
single system operating on 10 cm to answer both 
requirements. The so-called V-beam system, 
AN/CPS-6, the laboratory name of which was 
derived from its double beam, used an antenna 
system larger than that of any other American 
radar, consisting of one antenna giving a vertical 
fan beam for search and a second ‘‘slant” an- 
tenna giving a beam at an angle of 45° from the 
other. The range of the search beam was about 
200 miles ; the auxiliary antenna used conjointly 
with the other in height-finding was useful out 
to about 140 miles. Height-finding depended 


LIGHTWEIGHT HEIGHT FINDING RADAR 


69 


upon the fact that as the two beams scanned 
simultaneously a target was picked up first by 
the vertical beam and then by the slant beam, 
and the time difference depended only upon the 
slant range to the target and the height of the 
target. 

These antennas had multiple-horn feeds, pro- 
viding energy from a total of five magnetrons, 
and produced fan beams 1° wide in azimuth for 
fine resolution and 30° in elevation for all-alti- 
tude coverage. In addition to PPFs and B-scope, 
the V-beam system used a special height indica- 
tor which displayed the returning signals from 
both beams so that height could be read directly. 

Production and Testing 

The first laboratory V-beam system, in opera- 
tion by February 1944 at the Bedford Army Air- 
port, had all its components except indicators 
mounted on an old carnival merry-go-round mod- 
ified into a radar mount, the whole having the 
aspect of a giant back-of-dish installation. Tests 
at Bedford were so promising that the system 
was moved to Leesburg, Florida, for tests by the 
Army Air Forces Board during which the set 
demonstrated its ability to see through large 
quantities of “Window” in April 1944. On the 
basis of the satisfactory Florida tests, the Signal 
Corps officially requested MIT-RL to build 6 
preproduction models of the V-beam or AN/ 
CPS-6, and this order was later increased to 8. 
The Stone and Webster Company was given a 
contract to design a suitable mount. The mounts 
were manufactured according to this design by 
the Walsh Construction Company of Boston. 

The first mount was set up in a stockade near 
MIT Building 20 in December 1944. After a 
search of the Boston area to find a satisfactory 
site for erecting these large systems, it was de- 
termined to establish an Orlando Field Station 
of MIT-RL at Orlando, Florida, in January 1945. 
The first preproduction V-beam system was in 
operation from a 25-ft tower at the Orlando Field 
Station in March 1945. By October 1945, 5 of the 
8 sets had been completed — 3 stayed in this 
country for training purposes, 1 was shipped 
to the Pacific area and 1 to the Panama Canal 
Zone. In December 1944 a contract was let to 
GE by the Army for 60 production V-beam sets. 


5.6 LIGHTWEIGHT HEIGHT-FINDING 
RADAR, AN/TPS-IO 

The AN/TPS-10 project (MIT-RL “Little 
Abner”) filled the need for a lightweight radar 
which could be carried into mountainous country 
and be used to detect low-flying planes. In the 
laboratory, the TPS-10 was considered more as a 
detecting device than as a pure height-finder. In 
this light it was expected, as far as low-flying 
planes were concerned, to be a stop-gap for the 
slower moving program of the moving target 
indicator [MTI], a special attachment which 
was designed to wipe out ground clutter and pre- 
sent only the signals from moving targets on the 
indicator. MTI will be discussed later. Tactically, 
the TPS-10 was thought of in terms of experi- 
ence in the Italian Theater in late 1943 and in 
terms of experience in the Chinese and Burma 
Theaters. 

Design and Development 
Design Characteristics 

The TPS-10 set was designed to be broken 
down for hand-transport (with a few exceptions, 
no piece weighed more than 40 lb) and to produce 
(at 3 cm) a flattened pencil beam 0.7° in eleva- 
tion for height discrimination and 2° in azimuth. 
The beam “nodded” rapidly in elevation while 
scanning slowly in azimuth. The TPS-10 over- 
came the difficulty of ground clutter on the scope 
by using a single range-height indicator (adapted 
from the MIT-RL Beavertail indicator) which 
plotted elevation angle against range, thereby 
restricting clutter to the baseline of the scope. 

Tests of Experimental Models 

The project was undertaken in the winter of 
1943-44. An experimental laboratory TPS-10, 
assembled from available components, was tested 
at Bedford Airport by April 1944. Ranges were 
short (of the order of 30 miles) due partly to the 
low power of the modulator and partly to low 
receiver sensitivity. The tests indicated, how- 
ever, that with certain improvements ranges 
would be satisfactory. Between April and June, 
these chief improvements were made: electri- 
cally, a higher power modulator (borrowed from 
the HoK) and a more sensitive receiver (SO-SU 
type) ; mechanically, a new reflector and new 
elevation and azimuth movements. In July, this 


70 


SELECTED GROUND SYSTEMS PROJECTS 


improved Bedford model was moved to North 
Carolina for tests in hilly country. These tests, 
which were witnessed by representatives of the 
Army Air Forces and the Signal Corps, indicated 
that a medium bomber could be tracked at ranges 
of 40 to 50 miles with approximately 50 per cent 
success and that target discrimination was pos- 
sible where the target was separated from the 
ground by at least one beam width. 

Application 

On the basis of the North Carolina tests, the 
Army asked the laboratory to build 40 sets, to be 
preceded by 2 prototypes. The first of these was 
operationally tested by the AAFB at Leesburg, 
Florida, in November 1944, both separately and 


(for GCI) in conjunction with the AN/TPS-1, a 
portable U. S. Army search set. The second pro- 
totype, TPS-10, was tested mechanically at East 
Boston Airport and then sent to Warner-Robins 
Field, Georgia, where it was used for training 
Army personnel. Production of the 40 sets cov- 
ered the period from January to June 1945, with 
the manufacturing being done in the laboratory 
by officers and enlisted personnel who were later 
assigned to the sets. Besides being used for train- 
ing in the United States, TPS-lO’s went to 
France, Italy, Saipan, I wo Jima, and the CBI 
Theater. 

In February 1945, a letter of intent for 100 
sets (increased in April to 150) was given to the 
Zenith Radio Corporation, delivery to start in 
June 1945. 



Chapter 6 

AIRCRAFT RADAR SYSTEMS 


6.1 AIRCRAFT LANDING SYSTEMS, 

PGP AND GCA 

6.1.1 Origin of Theoretical Principles 

R eports from England of work on jamming, 
. beacons and blind landing resulted in the cre- 
ation of a group at MIT-RL, under the direction 
of Luis W. Alvarez, to study these problems. The 
group began to lay out a blind-landing program 
in September 1941. The accidental discovery 
that the experimental prototype of the SCR-584 
had twice been observed to follow airplanes all 
the way into a landing suggested the use of radar 
for blind landing. Alvarez had been following 
the preliminary experiments of the precision 
gunlaying group and conceived the idea that the 
directional properties of the conical beam might 
be used to define a straight-line path down which 
an airplane might fly. If the gunlaying equip- 
ment could be used, the only remaining problem 
was to devise a scheme by which the pilot could 
be given information of the magnitude and di- 
rection of his deviation from the predetermined 
glide path. 

6.1.2 Types of Systems Devised 

Two contrasting systems were ultimately de- 
vised. One resembled, in general outlines, the 
early MIT-RL continuous-wave system, but 
using a pulsed glide path, required receiving 
apparatus in the aircraft. The other, a ‘‘talk 
down’’ system, requiring no special gear in the 
aircraft except its normal communications sys- 
tem, was subsequently used in the ground-control 
of approach [GCA] radar. If, it was argued, a 
ground operator could tell so easily by radar the 
precise location of an incoming plane, why would 
it not be possible to convey this information to 
the pilot by radio telephone? 

6.2 PULSE-GLIDE-PATH SYSTEM 

6.2.1 Preliminary Experiments 

The first scheme explored was the pulse-glide- 
path [PGP] system ; and it was decided to test a 
rather simple version while waiting for the XT-1 


radar (a piece of equipment then much in de- 
mand) to be available for blind-landing tests. 
The ground transmitting system used a hori- 
zontal 10-cm dipole which was nutated through 
a 3-in. circle about the focus of a 48-in. para- 
boloid. The conical beam thus produced was di- 
vided into four distinguishable quadrants by 
switching the repetition rate every 90° by means 
of a mechanical commutator. The operation of 
the system was based on the fact that, in the re- 
ceiver aboard the aircraft, pulse repetition rates 
could be discriminated from one another by the 
use of suitable audio-filters. The amplitude of the 
signal strength in the various quadrants was 
compared by means of a cross-pointer meter. 
The line of equal signal strength corresponded to 
the desired glide path for the aircraft. After pre- 
liminary experiments during November and De- 
cember 1941, it was decided to use a 3-cm system 
and to install it in a truck for further tests. 

Report of Ad Hoc Committee on 
Instrument Landing 

sMeanwhile the director of OSRD appointed 
Alfred L. Loomis as chairman of a committee 
known as the “Ad Hoc Committee on Instrument 
Landing” to study the military aspects of blind 
landing, to consider the future needs of the Serv- 
ices and to recommend programs of research and 
development. The committee was also directed 
to consider the British requirements. 

The committee, consisting of Army and Navy 
representatives as well as NDRC members, held 
its first meeting on December 4, 1941, and issued 
its final report on February 16, 1942. Luis W. 
Alvarez and Donald E. Kerr of MIT-RL studied 
all existing blind-landing systems, British as 
well as American, and submitted a report which 
was edited by E. L. Bowles, Secretary of the 
Microwave Committee. The Ad Hoc Committee 
on Instrument Landing reported that the Army 
had found no solution for the instrument landing 
of fighter types of aircraft and that the Navy had 
no system in prospect for carrier landings. The 
Navy placed emphasis on the need for a uni- 




71 


72 


AIRCRAFT RADAR SYSTEMS 


fied system for all Services. The committee rec- 
ommended that MIT-RL explore as intensively 
as possible the application of some GL “talk 
down” method of instrument landing since most 
aircraft could not be burdened with receivers. 
Also the laboratory was advised to continue the 
pulse-glide-path work to fulfill immediate Army 
requirements. 

Tests of PGP System 

By Army request the PGP system was demon- 
strated, in conjunction with two other systems, 
at Indianapolis, Dayton, and Pittsburgh, in the 
presence of representatives of the Army, Navy 
and the British Air Commission from Septem- 
ber 15 through November 26, 1942. The outcome 
of these tests was a recommendation by the 
Army that the Sperry Gyroscope Company un- 
dertake production of a glide-path system based 
upon MIT-RL equipment, for it seemed that this 
might be produced sooner than any other. Sperry 
agreed to undertake the development and the 
laboratory’s truck was sent to Garden City for 
study. 

The laboratory had previously ordered some 
models of the PGP equipment from the Delco 
Radio Division of General Motors to serve as 
prototypes. The first Delco model was tested in 
East Boston from January 12 to February 5, 
1943. The laboratory’s participation in this proj- 
ect ceased with these tests. Because Sperry did 
not display marked interest in the system, and 
because the Army did not push the project with 
any enthusiasm, this equipment never reached 
production. In the meantime the possibilities of 
a talk down system were being explored and 
the blind-landing program eventually proceeded 
along these lines. 

63 talk down system (GCL) 

6.3.1 Preliminary Investigation 

In April 1942, the XT-1 truck was made avail- 
able for blind-landing experiments. For about 
two months (April and May 1942) tests were 
carried out. The results were, on the whole, 
rather poor. The GL antenna, except under 
anomalous conditions, would not give low enough 
coverage to land airplanes. It was evident that a 
special radar must be designed if a talk down 


system were to be feasible. The solution to the 
problem came with the decision to use the linear- 
array antenna, recently invented for MEW, and 
the radar bombsight. Eagle. The landing project 
then started off in another guise as ground-con- 
trol landing [GCL] . 

Mark I Experimental System 

Components, By July 1942, an experimental 
system was set up at the East Boston Airport and 
designs were drawn up for two trucks to house 
the Mark I system. The antenna truck housed 
two 3-cm antennas of the “leaky-pipe” variety 
with cylindrical paraboloid reflectors. A vertical 
antenna scanned in elevation and fed a PPL A 
horizontal antenna of the same variety scanned 
in elevation and fed another PPL These scopes 
were later replaced by B-scopes. The power sup- 
ply and r-f system took up the rest of the space. 
The control truck housed the indicators and op- 
erators, the communications equipment and a 
10-cm PPI radar search system for traffic con- 
trol. A “director” mechanism for indicating devi- 
ation of a plane from an ideal flight path was 
later added. 

Functional Purposes. The equipment was de- 
signed to perform two functions. First, when one 
or more aircraft are to be landed the search radar 
can “stack” all but the one plane to be landed and 
keep the others circling in a traffic pattern about 
the field ; second, the precision units provide the 
operators with continuous information as to the 
position of the plane and precise instructions are 
given to the pilot over the air-ground communi- 
cations system so that he is “talked down” to a 
point which is in line with the runway. No extra 
equipment has to be carried in the airplane. 

Performance of Experimental Models 

While improvements in the Mark I system, to 
make it compact enough for one truck, were in 
progress, the two-truck system was taken to the 
Naval Air Station at Quonset Point, Rhode 
Island. On December 26, 1942, the first com- 
pletely blind landing under control of GCL was 
flown by a Navy SNJ aircraft piloted by Ensign 
Bruce Griffin, USN. Several hundred successful 
landings were flown here and the results led the 
High Command to request a demonstration at 
the National Airport in Washington in February 


TALK DOWN SYSTEM (GCL) 


73 


1943. The AAF immediately afterwards decided 
to initiate quantity production of this system. 
The British Air Commission requested that the 
trucks be sent to England for demonstration. 

6.3.2 Development of Mark II System 
Early Tests and Improvements 

Before any Army or Navy contracts had been 
considered the OSRD had entered into a develop- 
ment contract with Gilfillan Brothers Company 
for the manufacture of 10 systems which the 
laboratory felt might be allotted to the Services 
for experiment and training. Gilfillan engineers 
came to the laboratory soon after July 1942 when 
research was in the initial stages and they par- 
ticipated in early tests. In the early fall of 1942 
steps were taken toward the development of a 
second version, called Mark II. The principal im- 
provement was the introduction of the scanning 
array which was showing good results in the 
Eagle program. Two prototype arrays, an 8%-ft 
and a 14-ft, were tested in the early spring of 
1943. A newly designed precision indicator was 
also added. The Mark II system was planned for 
one truck and a trailer. 

Several conferences were held at Camp Evans 
Signal Laboratory and specifications were 
drawn up with the help of MIT-RL members. 
The Army decided to make Gilfillan its prime 
contractor and the joint U. S. Army-U. S. Navy 
designation AN/MPN-1 was given because the 
Navy also ordered equipment from the Bendix 
Radio Division in Baltimore. At MIT-RL the 
short title was changed to ground-control of ap- 
proach [GCA] since the military characteristics 
merely required the placing of an incoming air- 
plane over the runway at an altitude of about 
thirty feet from which point a visual landing 
could usually be made. 

Field Performance 
British Experience 

The old Mark I system, accompanied by RL 
members, was sent to England for trials by the 
RAF during July and August 1943. On August 
23, the GCA landed 21 Lancasters returning from 
a raid in one hour and thirty-eight minutes. 
Only 4 failed to make satisfactory approaches 
and land at the first attempt. 


After the final RAF operation. Group Captain 
Saker, officer in charge of trials, decided to rec- 
ommend that all contracts for other approach 
systems be stopped and the American GCA 
adopted instead. 

Production and Distribution 

The first production unit of Mark II GCA was 
undergoing preliminary field tests during the 
month of January 1944. A total of 236 GCA’s 
were delivered before the end of the war : 112 to 
the Army by Gilfillan Brothers Company, 49 to 
the Navy by Bendix Radio Division, and 75 to the 
U. S. Army by Federal Telephone and Radio 
Corporation; but the sets were slow in getting 
into combat use. 

U. S. Installations. By the end of the war Air 
Transport Command had GCA sets operating in 
Iceland; in the Azores; at Gander Field, New- 
foundland; Presque Isle, Maine; and others of 
its bases. Similarly U. S. Naval Air Stations in 
the United States at Quonset Point, Rhode 
Island; San Diego, California; Alameda, Cali- 
fornia; and Whidbey Island, Washington (Seat- 
tle) , were equipped with GCA and about 20 more 
installations were planned. 

European Installations. In Europe, theater re- 
quests did not keep pace with the available sup- 
ply of sets. Two GCA’s were in use in the Medi- 
terranean Theater : one at Fano,the other at Pisa. 
In the European Theater of Operations General 
O. P. Weyland was especially anxious, in Jan- 
uary 1945, to have each wing and later each 
group of the Tactical Air Forces and the Air 
Transport Wings equipped with a GCA. At that 
time an allotment plan for 12 sets was drawn up 
but as it turned out only 8 sets were operational 
by the time of German surrender. Three of these 
were operated by the Eighth Air Force in Eng- 
land. The firs,t set to go into combat on the Conti- 
nent was located at A-82 (the night-fighter field) 
near Verdun, under the Nineteenth TAC. 

Early in February 1945, before the regular 
crew had arrived and before the set was really 
considered operational, a skeleton crew of two 
BBRL men and a special installation crew of 
four Signal Corps men landed, under emergency 
conditions, a C-47, two P-61’s and a flight of 
P-47’s. This equipment was later moved into 
Germany. Another was the set under control of 


74 


AIRCRAFT RADAR SYSTEMS 


the Ninth TAG, at Florennes (field A-78), near 
Charleroi, Belgium ; this was also moved to Ger- 
many. The Ninth Bombardment Division of the 
Ninth Air Force operated a GCA first at 
Peronne, France, later at Venlo, Holland (field 
Y-55). A seventh unit, under the Twelfth TAG 
was used first at Luneville, France, then in Ger- 
many. An eighth unit was put in operation 
at the end of April 1945 near Munster, Germany, 
with the Twenty-ninth TAG. Over 40 emergency 
landings were safely carried out by these first 
few GCA sets to go into operation. 

Pacific Theater Installations. There were no 
GCA's in the China-Burma-India Theater but 
quite a number were installed or on their way to 
other locations in the Pacific Ocean area by the 
time war ended. The Army had sets operating on 
Iwo Jima, Leyte, Okinawa, Tinian, and Saipan. 
The Iwo Jima GCA saved several lost or dam- 
aged aircraft, including some B-29's returning 
from raids on Japan. Sixteen or more sets and 
16 trained crews were en route to planned in- 
stallations in the Aleutians, Guam, and elsewhere 
in the Pacific at the conclusion of hostilities. 

6.4 NAVIGATIONAL AND BOMBING 
RADARS, NAB AND HsX 

6.4.1 Development of NAB and H 2 S Systems 

From the summer of 1942 to the end of the war 
the MIT-RL devoted a steadily increasing share 
of its manpower to the development of radar de- 
vices for high-altitude bombing through over- 
cast. In June 1942 work began under J. W. Miller 
on a device referred to as navigational aid to 
bombing [NAB]. It was a 10-cm system based 
on ARO techniques, using a lighthouse tube 
(since it was considered undesirable to fly mag- 
netrons over enemy territory) , a PPI, and a cut- 
paraboloid antenna with a 360° scan. Its use was 
based upon a recent observation that cities gave 
stronger echoes than open country. The first 
NAB system was installed in a B-18 airplane in 
October and flown unsuccessfully, for it did not 
give the desired discrimination. 

Improvements on Original NAB 

In December, when G. E. Valley became proj- 
ect engineer, it was decided to replace the light- 


house tube with a magnetron. NAB was now a 
modification of the ASV with a newly developed 
antenna providing what is described as a cose- 
cant squared (esc-) pattern. Even with this im- 
proved system, cities (except those with land- 
water contrast) were hard to identify, so it was 
decided in January 1943 to change to 3 cm. This 
made NAB essentially a 3-cm version of what 
the British were calling H 2 S. 

Experiments on H2S 

Work on the necessary 3-cm r-f components 
was delayed by the low priority acquired by NAB 
as a result of the conference on radar bombing 
held at the MIT-RL on February 13, 1943. Dale 
R. Corson and N. F. Ramsey, both civilian repre- 
sentatives of the AAF, and David T. Griggs, of 
the Office of the Secretary of War, all gave 15-20- 
mil bombing accuracy as the Army's require- 
ment for any radar bombing aid. This somewhat 
visionary accuracy was in no sense claimed for 
NAB. 

However, Valley believed in his system and 
work continued after 3-cm r-f components were 
received in April. As a result, H 2 X was in ex- 
istence when Griggs came back from England, 
where he had been investigating British blind 
bombing at the request of Robert A. Lovett, As- 
sistant Secretary of War for Air. He brought 
with him requests from the Eighth Air Force to 
back this demand for the delivery of twenty 3-cm 
sets by September 1. The improved resolution of 
H 2 X was a result of its higher frequency and the 
improved ASD-1 receiver. 

Final Design 

Production Program. Early in June a program 
under joint Army-Navy sponsorship was set up. 
MIT-RL undertook a crash program of 20 sets 
to be delivered to the Army Air Forces by Sep- 
tember 1943. This was under the direction of G. 
E. Valley and Lt. (j.g.) R. L. Foote, USNR. The 
laboratory was also to furnish engineering in- 
formation and advice to Philco, which was to 
produce the AN/APS-15 for the Navy. Later 
the laboratory agreed to act as advisor to BTL 
for the Army's AN/APQ-13. 

Model Components. The H 2 X and AN/APS-15 
consisted of the ASD r-f assembly, the ASG spin- 
ner base, the ASG-3 indicator central, and the 


EAGLE HIGH-RESOLUTION RADAR, AN/APQ-7 


75 


ASD-1 receiver, special 3-cm r-f components and 
an improved esc- antenna, and HoS ranging cir- 
cuits. The AN/APQ-13 was identical except for 
the use of 717-T3 components. 

Improvements Following Distribution. By- 
August one H 2 X set had been installed in a B-17 
aircraft. By September 15 all 20 sets were com- 
plete, and the required 12 were installed in 
B-17's. Philco production began in October. The 
total Philco production, including modifications 
(AN/APS-15A and B) was 7,835 sets. The total 
Western Electric production of AN/APQ-13, 
begun in December 1943, was 10,995. 

Training began at Grenier Field in August 
under the direction of Griggs. During training 
it was discovered that r-f breakdowns occurred 
at high altitudes. MIT-RL men went to Grenier 
Field and installed the pressurized r-f system 
that had been originally designed. The later sets 
were pressurized. In November, a crash training 
program was set up at Langley Field, using H 2 X 
systems in airplanes, and AN/APS-15 sets on 
the bench. By October the first of the crash sets 
had arrived in England, accompanied by two 
members of the original MIT-RL H 2 X group, 
D. Halliday and S. McGrath. 

6.5 EAGLE HIGH-RESOLUTION 

RADAR, AN/APQ-7 

Requirements of High-Altitude 
Blind-Bombing Device 

Work on Eagle, planned as a precision, ra- 
dar high-altitude blind-bombing device, began 
in November 1941. The central idea was to pro- 
duce a set having extremely high resolution 
using the highest frequency then available. High 
resolution would be obtained by increasing as 
much as possible the gain of the antenna, rather 
than waiting for techniques to be developed at 
shorter wavelengths. 

As a result of a conversation with E. G. Bowen, 
British liaison representative at the MIT-RL, 
L. W. Alvarez realized that a practicable radar 
bombsight need have high directivity in only 
one plane, and hence required a refiector large in 
only one dimension. As Alvarez worked it out 
toward the end of November, the system would 
operate on 3-cm, and the distinguishing feature 
of the system would be a linear-array, leaky-pipe 


(slotted waveguide) diffraction grating 20 
ft long, mounted along the leading edge of a 
bomber wing. Some device would have to be 
worked out to scan the beam, by changing the 
electrical properties of the array. It was hoped 
that the accuracy of such a set would approach 
that of the Norden sight, then erroneously 
thought to be capable of 15-mil bombing. 

Development of Components 
Experiments With Fixed Antennas 
By February 1942, a nonscanning antenna had 
been built and tests on the antenna pattern were 
made with very disappointing results, since 
three distinct lobes were obtained instead of a 
single beam. In March, the antenna problem was 
assigned to R. M. Robertson, and various more 
or less successful methods of eliminating the ex- 
tra lobes were obtained. By the end of April a 
leaky pipe antenna had been devised that gave 
a narrow beam free from large secondary lobes. 

In May, Alvarez conceived the idea of the re- 
versed dipole array for use with Eagle and 
MEW. By reversing alternate dipoles it is pos- 
sible to reduce the dipole spacing sufficiently to 
give a single beam. For use with Eagle this could 
be scanned by varying the cross section of the 
waveguide. There was a good deal of scepticism 
about the practicability of such a long array as 
had originally been proposed ; it was felt that a 
20-ft array would be quite impossible to align 
and that phase errors would be enormous. A 13- 
ft fixed antenna was therefore built and tested ; 
it gave a good pattern with a beam width of less 
than half a degree. 

Development of Scanning Antenna 
For some time scepticism remained strong 
within the laboratory, except within the Eagle 
group itself, so much so that they were forced 
to work with low priority. In consequence much 
shop work was done by outside firms. With the 
promise of a workable antenna the Eagle Proj- 
ect then variously known as radar bombsight 
[RBS], bombing-through-overcast [BTO], and 
more picturesquely as every-house-in-Berlin 
[EHIB] (indicating the accuracy expected) was 
formalized as a laboratory project with E. A. 
Luebke as project engineer. He undertook to 
have a 3-ft scannable antenna constructed, while 


76 


AIRCRAFT RADAR SYSTEMS 


in July the indicator group under W. A. Higin- 
botham began work on an indicator. This was to 
have accurate ground range sweeps combined 
with computer circuits, together with an ex- 
panded indicator for bombing. 

Computer 

During the fall of 1942 the idea of a separate 
computer came into favor ; the Norden Mk XV, 
the General Electric, the Librascope, the Bell 
Laboratories BTO computer, and finally BelFs 
universal bombsight [UBS] , were all considered. 
Parallel development on circuits for use with all 
these computers went on for a year. It was rec- 
ognized that the first goal should be a simple 
straight-line computer with a stabilized indica- 
tor giving an accurate map of the ground. 

Test of Scanning Antenna 

In the summer of 1942 the 3-ft, variable width 
waveguide scanner was tested ; the pattern was 
poor and losses high, but it radiated and scanned. 
The 6-ft antenna, tested in November, had im- 
proved chokes, but still a limited scan. The idea 
of alternate end feed, with an r-f switch, was 
then developed and incorporated in the 8-ft an- 
tenna, which also had improved dipoles. After 
completion of the 8-ft antenna in February 
1943, the final production size, a 16-ft antenna 
was next tried. This was delivered in March, and 
after a few changes was satisfactorily tested in 
May. 

In October 1942 Robertson thought of mount- 
ing the antenna in a wing-shaped fairing or vane 
under the airplane, instead of in the leading 
edge of the wing. A plywood vane was designed 
at MIT-RL and built by the F. J. Hagerty Co. 
This vane was attached to a B-24 at Wright 
Field in May 1943 and the plane was then suc- 
cessfully flown to Westover Field for installa- 
tion of the 16-ft antenna. 

During the spring of 1943 work was rushed 
to permit early flight tests, under the guidance 
of J. H. Buck, and steps were taken toward pro- 
duction. Early in 1941 the Army had assigned 
the project number AC-1 to Eagle, an indication 
of the importance of a precision radar bombing 
device. In March 1943 the Materiel Command 
formalized the program, recommending West- 
ern Electric, in the interests of standardization, 
as the contractor. A contract for 5 systems, with- 
out computers, was given to Western Electric 


in May with the designation AN/APQ-7. At this 
time there was an Army-Bell-Radiation Labora- 
tory conference, the first of many, to define 
Eagle. The Army wanted a short-range project 
with a simple straight-line computer but with 
the UBS Eagle as the ultimate goal. As at many 
other conferences during the next two years, the 
relationship of Eagle to the overall bombing 
program was discussed. Many times it was sug- 
gested that Eagle be cancelled in favor of HAB 
or AN/APQ-10, or later in favor of K-band. 

In April 1943 an NDRC contract was given to 
the Douglas Aircraft Co. for the development of 
a vane. In May, Eagle became the first project 
to have the full-time services of a transition 
office man. J. W. Eggers contributed much to 
Eagle, especially in coordinating the antenna 
and vane production. He also became very much 
interested in an interim, simple Eagle, which 
would permit the use of the high resolution of 
the Eagle antenna long before the UBS program 
became a reality. In June a group of Bell engi- 
neers came to work with the various Eagle 
groups in MIT-RL, a beginning of the close co- 
operation between the two organizations, and 
in July, a Douglas engineer came for the same 
purpose. 

Results of Flight Tests 

On June 16, 1943, Eagle was given its first 
flight test at Westover Field. The resolution was 
all that was expected, though there were some 
troubles with the r-f switch and the flaps which 
shaped the vertical pattern. However, the elec- 
trostatic tube required for the completely stabi- 
lized, accurate sweeps in the indicator gave very 
poor contrast, and the complicated circuits were 
unstable. It was replaced with a simple sector 
PPI magnetic tube, which gave a satisfactory 
presentation of the high resolution afforded by 
the antenna. This installation was shown to the 
Army. Although a complete indicator, with sta- 
bilized sweeps and an expanded indicator, was 
working on the roof of Building 24, Luebke, 
Eggers, and Robertson urged on the Army the 
advantages of a simple Eagle with magnetic 
tube. 

6.5.3 Design and Specifications of Mark I 

In August, Western Electric received an order 
for 50 AN/APQ-7’s, and it was necessary to de- 


EAGLE HIGH-RESOLUTION RADAR, AN/APQ-7 


77 


cide exactly what an AN/APQ-7 set was. Dis- 
cussions involving the U. S. Army, MIT-RL, 
and BTL culminated in a conference on October 
22, 1943, at which the simplified Eagle Mark I 
was chosen, in spite of opposition. The Bell en- 
gineers did not want to give up the tie-in with 
their UBS, and certain of the MIT-RL indicator- 
computer people naturally disliked the shelving 
of all the effort they had put in. In fact, work 
continued hopefully on the UBS project for some 
months. Eagle Mark I consisted of a 16-ft an- 
tenna, a 717-T3 modulator and r-f head, a modi- 
fied 717 receiver, an impact predicting computer, 
and an indicator with approximate ground range 
sweeps. BTL accepted an order for 40 prepro- 
duction sets, to start in April 1944, with Western 
Electric production of 612 sets to start in July 
1944. MIT-RL agreed to act as the Army’s con- 
sultant, and close liaison was maintained with 
Bell until the end of the war. 

Eagle became the first radar set designed by 
RL for which complete specifications were set up 
before production. The design objective was set 
at 80 mils bombing accuracy, a figure bettered in 
production. In November, Douglas agreed to 
continue work on the B-24 installation, while 
plans were made for a B-29 installation. When 
Western Electric, arguing that it was not in the 
airplane business, asked to have the wings and 
leading edges supplied by the government. Di- 
vision 14, at the Army’s request, initiated an 
OSRD contract with Douglas for 50 preproduc- 
tion wings. The Radiation Laboratory then as- 
sisted Bell Laboratories and Western Electric in 
finding a suitable manufacturer for the antenna. 
Ex-Cell-0 Corp., Detroit, was chosen in Decem- 
ber 1943. . 

Flight Test Results 

The MIT-RL B-24 with a Mark I indicator 
went to Boca Raton, Florida, for the winter 
where extensive flight tests were made to deter- 
mine bombing accuracy, and the suitability of 
the equipment for navigation and for measuring 
ground speed and drift. Operation was quite 
satisfactory, and such bombing as was done was 
well within the specified accuracy. 

In March 1944 there was a temporary crisis 
in Eagle production. Western Electric declared 
that no sets would be produced that year unless 
the Army furnished considerable help. At the 


March meeting of the Stratton Committee, an 
attempt was made to have Eagle cancelled in 
favor of K-band, which was claimed to have al- 
most as high resolution, and had a 360° scan. 
The 60° scan of Eagle had always been severely 
criticized, and sections of the Army remained 
opposed though navigation proved to be not es- 
specially difficult in practice. However the Eagle 
Mark I program was kept intact, though Eagle 
Mark II (with AN/APA-44) and Eagle Mark III 
(with the UBS) were cancelled. Shortly after 
this Western Electric determined that it would 
be possible to meet production schedules. 

On May 16, 1944, the first BTL preproduction 
set was successfully flight-tested. The flight 
model was sent to the Aircraft Radio Field Lab- 
oratory at Boca Raton for tests ; acceptance tests 
were finished by fall. In September the Bell pre- 
production order was complete, ahead of sched- 
ule, and Western Electric, whose order had been 
increased to 1,660 sets in June, began production. 

Modifications and Applications 

During 1944 and 1945, MIT-RL worked on 
various attachments and modifications for Eagle. 
Camera attachments for taking scope pictures 
were designed by the laboratory and 25 of them 
were manufactured by RCC. A supersonic 
trainer was designed in the laboratory in 1944, 
and produced by RCC early in 1945. AN/APQ- 
16, Eagle with GPI, had been under considera- 
tion for some time at the end of the war. Plans 
had been made for mounting the Eagle antenna 
in the wings of future heavy bombers, B-32 and 
B-36, with the possibility of an Eagle antenna 
in each wing to increase the scan angle. Some 
inconclusive tests were made in the summer of 
1944 on the use of Eagle for tank reconnais- 
sance. Eagle was successfully used for blind- 
approach landings, and there were discussions 
of the use of Eagle in control of guided missiles 
(war weary aircraft). 

6.5.4 Training and Test Programs 

In the late summer of 1944 attempts were 
made to equip planes of the Eighth Air Force 
with Eagle. Considerable difficulty was met in 
this attempt, partly because the U. S. Army, re- 
acting from the H 2 X crash program, insisted 
that the Eagle program be orderly, and partly 
because the Twentieth Air Force had priority 


78 


AIRCRAFT RADAR SYSTEMS 


for its B-29’s. Finally one Eagle B-17 was ob- 
tained, and arrived in Alconbury in October 
1944. Buck went to England to assist in testing 
and setting up training facilities. The set, when 
it arrived, was found to have a bad hole in the 
pattern, which was corrected by careful adjust- 
ment of the flaps. An intensive program at RL 
was initiated to correct this situation. It was 
found that rigid control of tolerances was re- 
quired so that Western Electric was persuaded 
to accept overall supervision of the vane and 
scanner manufacture and installation. In Eng- 
land flight tests were carried out, and a training 
program set up for operators and mechanics in 
the theater. 

Boca Raton Training Program 

The first Eagle training school, for operators 
and mechanics, was set up at Boca Raton in 
December 1944, with assistance from MIT-RL. 
The laboratory trained the instructors, and also 
prepared a training movie for the mechanics. 
When training began in the Second Air Force 
for the 315th and 316th wings of the Twentieth 
Air Force, the MIT-RL cooperated extensively. 
The operators were given basic training at Boca 
Raton and at Williams Field, advanced training 
at Victorville, and crew training at Second Air 
Force bases. The MIT-RL men worked to im- 
prove crew training. In addition one man from 
the laboratory was stationed at the headquarters 
of the 316th wing and one at each of the four 
groups in the wing. MIT-RL also trained the 
personnel in the Bowditch Project of photo re- 
connaissance. This was the first time an exten- 
sive program of scope photography of intended 
targets was undertaken before actual operations 
began. 

Tests at Orlando 

Almost the only program in which the labora- 
tory did not assist was the AAF Board tests at 
Orlando in the beginning of 1945. The men con- 
ducting this program were H 2 X operators who 
knew little of Eagle and disliked the limited scan. 
They solicited no help or advice from either the 
laboratory or BTL. After somewhat limited 
tests, using poorly conceived bombing proced- 
ures, they turned in a most unfavorable report, 
though they admitted that Eagle had a higher 
bombing accuracy than other bombing radars. 


This adverse report may have delayed the opera- 
tional use of Eagle, but did not prevent its event- 
ual use. 

Field Application 

Although just too late to become operational 
in Europe, Eagle was used in several successful 
B-29 strikes by the 315th wing in the Pacific. 
The bombing of the Maruzen oil refinery on July 
6-7, with 95 per cent destruction, was the most 
spectacular of these operations. General LeMay, 
in a telegram of commendation said “This per- 
formance is the most successful radar bombing 
of this command to date.” 

6.6 BLIND BOMBING AT SEA, AN/APQ-S 

Initiation of LAB Project 

A most significant by-product of the labora- 
tory’s first participation in the antisubmarine 
campaign was the development of equipment 
permitting low-altitude blind bombing of ship 
targets. One of the men of Colonel Dolan’s First 
Sea Search Attack Group proposed to MIT-RL 
staff members who were stationed at Langley 
Field to keep the equipment in running order, 
that a device permitting the bombing approach 
to be done “blind” would be of inestimable value. 
The development was undertaken, and in a 
month or two an experimental attachment, in 
the form of a simple computer with its own indi- 
cator that tied in to the optical bombsight, was 
ready for test. The experimental drops, made at 
Langley Field in October 1942 and later at Eglin 
Field, Florida, were so successful that it was 
resolved to give this equipment serious con- 
sideration. A development contract for this de- 
vice, usually referred to as loiv -altitude bombing 
[LAB] or as AN/APQ-5, was given to the BTL. 
The Bell engineers were shown the MIT-RL 
equipment and in their own development fol- 
lowed the fundamental approach without devia- 
tion but substituted their own computer circuits 
and designed the device for use with the Western 
Electric SCR-717 equipment. Proof tests were 
run on the AN/APQ-5 in April 1943 with RL and 
BTL personnel cooperating. 

6.6.2 Performance in Pacific Theatre 

The first of these radar sets saw combat, on 
what was distinctly more than an experimental 


BLIND BOMBING AT SEA, AN/APQ-S 


79 


basis, against Japanese shipping in the South 
Pacific in 1943 and 1944. The first squadron of 
Liberator bombers equipped with the SCR-717 
and the APQ-5 reached its Pacific base in August 
1943. It had been organized and trained at Lang- 
ley Field by Col. Stuart P. Wright, A.C., who 
had been attached to MIT-RL as Air Forces 
liaison officer during the period of LAB develop- 
ment. With this equipment the Army Air Forces 
were able to enforce an interdiction campaign 
that together with the attacks of submarines, 
virtually severed Japanese communication lines 
to their South Pacific outposts. 

Since an uninterrupted supply system is es- 
sential in island warfare, one of the primary 
tasks of the U. S. forces in the Pacific was stra- 
tegically to blockade Japanese merchant ship- 
ping lines. When convoys were reported, large- 
scale daylight attacks could be made, the opera- 
tions being well worth the number of planes 
required. However, over half the J apanese ship- 
ping sunk in the Pacific had been operating, not 
as convoys, but as single ships which entered 
patrolled waters after dark. Since a patrol can 
carry only a limited number of bombs due to the 
vast distances it must travel, it must be able, 
upon sighting an enemy ship, to score on the 
first, or at most, the second run. This is a difficult 
and complicated assignment, especially at night, 
since the target is small, the bomb load limited, 
and evasive action sure to be taken. 

Old antishipping technique, in which bombers 
ffying in daytime sweeps bombed from medium 
and high altitudes, required a prohibitive num- 
ber of planes. But single “snoopers,” equipped 
with SCR-717 and LAB, and patrolling by night 
the known Japanese shipping lanes, could sur- 
prise the radarless, poorly defended merchant- 
men and barges, and, coming in under condi- 
tions of zero visibility at altitudes of approxi- 
mately 1,000 ft strike before evasive action 
could be taken or defenses manned. 

Three such squadrons of snoopers are 
known to have operated in the Pacific, one with 
the Fifth Air Force, one with the Thirteenth, and 
one with the Fourteenth. The Thirteenth Air 
Force was the first to receive a squadron with 
LAB and to introduce the new equipment into 
combat. In late August 1943 after a two months’ 
period of intensive training at Langley Field, 


Colonel Wright, with a selected group of pilots, 
navigators, bombardiers, and technicians, and 
ten LAB B-24’s arrived at Thirteenth Air Force 
Headquarters at Espiritu Santo in the New 
Hebrides and then moved on to Guadalcanal. 
Colonel Wright remained with his group ap- 
proximately one month. During this early opera- 
tional period of 67 combat missions flown, 46 
bombing runs based on radar contacts were made 
with 17 direct hits. The Wright Project was 
transferred to the 868th Bombardment Squad- 
ron which was for a short time based at the 
Munda Air Base in New Georgia, and which con- 
tinued its antishipping depredations until fairly 
late in the war when, because of the scarcity of 
enemy shipping, it became a general purpose 
bombing force. 

Colonel Wright might also be considered re- 
sponsible for the second LAB squadron that left 
for the South Pacific. In October 1943, Lt. Col. 
Edward W. Scott, who had earlier been con- 
vinced by Colonel Wright of the potentialities 
of the LAB project, took 12 B-24’s with their 
specially trained crews out to the Fifth Air 
Force. There, as the Sixty-third Sea Hawk 
Squadron of the Forty-third Bombardment 
Group they operated in the Rabaul-New Hanover 
area, extending their territory north and west to 
Mindanao later in the same year. During a cross- 
sectional period of four months, this squadron 
made an impressive record, accounting for 32 
per cent of all ships sunk by the Bomber Com- 
mand. In so doing, the squadron used one-fourth 
the number of planes, bombs and personnel, the 
rest of the Command employed in its entire anti- 
shipping activity. For attacks against shipping, 
the effectiveness of the LAB squadron was ap- 
proximately 400 per cenf greater than that of the 
rest of the Command’s aircraft not so equipped. 
By spring of 1944 the targets available to the 
Sixty-third Sea Hawk Squadron had become lim- 
ited, for the enemy was using only smaller vessels 
with shallow draft and was operating them close 
to shore. 

Admirable as were the records of the Fifth 
and Thirteenth Air Forces in their nighttime 
interdiction work, that of the Fourteenth was 
still more impressive. The Fourteenth’s LAB- 
equipped 308th Group (H) operating under Lt. 
Col. William D. Hopson during the summer of 


80 


AIRCRAFT RADAR SYSTEMS 


1944 in the China Sea had the advantage of by 
far the largest amount of Japanese shipping. It 
-was estimated that from 750,000 to 1,000,000 
tons of Japanese shipping passed within range 
of the 308th’s bombers each month and the group 
was able to average the extraordinary figure of 
three sightings and 1,200 tons sunk per sortie. 
Unfortunately the number of planes available to 
the group was inadequate to deal with the traffic 
density and two out of three targets picked up 
in the China Sea went untouched. In spite of the 
shortage of planes, however, during the first 
three months of Hopson’s Project, 113,400 tons 
of cargo vessels and 7 warships were sunk and 
another 54,300 tons damaged, while during the 
month of September, a record score of 110,000 
tons or 1,700 tons per sortie was chalked up. 

6 7 AIRBORNE GUNLAYING SYSTEMS, 
AGL-I AND AGL.2 

6.7.1 Initiation of AGL Project 

The development of gunlaying systems [AGL] 
were first seriously considered at MIT-RL as a 
result of a request from General Arnold to E. L. 
Bowles, at that time secretary of the Microwave 
Section of NDRC. As a result of this request 
Bowles accompanied by L. N. Ridenour attended 
a conference at the Douglas Aircraft Company 
at El Segundo, California, early in July 1941. 
The Air Corps as well as the Douglas Company 
was anxious to have radar equipment installed 
in the new attack bomber, the XA-26A. The 
mockup of the aircraft was based on the use of 
the AI-10, but Douglas representatives, particu- 
larly F. R. Collbohm, wanted a more elaborate 
fire-control radar, since.the plane was to carry a 
computer which would make firing of the guns 
accurate beyond point-blank range. It was de- 
cided that Douglas should plan on an AI-10 in- 
stallation, but GE was given a contract to modify 
this equipment for gunlaying, and in August the 
AGL-1 project was officially started at MIT-RL. 

Characteristics of AGL Systems 
AGL-1 Model 

AGL-1 was a 10-cm system derived from the 
AI-10, which permitted search, automatic track- 
ing, and blind firing against enemy planes at 


night. After the operator selected the target, the 
system locked on it, and thereafter automatically 
supplied azimuth, range, and elevation data to 
the computer which directed the movable tur- 
rets. It was designed primarily for the XA-26A, 
and secondarily for the P-61. Various forms of 
antenna were developed, and there was some 
work on an AGL-1 Mark II, a lighter weight 
version. By January 1942 the system was operat- 
ing on the ground, and was soon after flown in 
a B-18. Flight tests were successful enough to 
persuade the Signal Corps to order 200 sets from 
GE of a production version called the SCR-702A 
(later AN/APG-2). This was followed in Janu- 
ary 1943 by an order for 200 sets of the SCR- 
702B (AN/APG-1) from Western Electric. 

AGL-2 Model 

By January 1942 plans were being made for 
several other types of airborne gunlaying equip- 
ment in all of which MIT-RL took some part. 
AGL was, however, always a small project, with 
rather low laboratory priority. The AGL-2 
(SCR-580) was a 3-cm system being undertaken 
by the Sperry Gyroscope Company, intended for 
use in the XB-29. MIT-RL started work on this 
in May 1942, and tested a system made up of 
parts supplied by Sperry. The first Sperry sys- 
tem was given flight tests at Eglin Field early 
in 1943, and the contract was terminated in May 
1943, when other systems appeared more promis- 
ing. The AGL-3, a 3-cm system for installation in 
a U. S. Navy PB2Y-3 was almost entirely a 
Sperry development, though MIT-RL gave some 
advice. The AGL-4 was a 3-cm system to provide 
very accurate ranging for the 75-mm cannon in 
the XA-26B. This modified form of the AI-3 was 
flown in an AT-11 plane at MIT-RL in March 
1943, but the project was cancelled soon after. 
The AGL-5, for the XP-71, never was developed 
for want of a plane. 

AGL-3 Model 

Despite all this va-eUvient, the only AGL sys- 
tems produced in quantity were the AN/APG-1, 
at Western Electric, and the AN/APG-3, a rela- 
tively lightweight set for B-29’s, at General 
Electric. GE’s contract for the AN/APG-2 was 
cancelled in October 1944, partly to prevent inter- 
ference with the AN/APG-13 (Falcon), and 
partly because the AN/APG-3 was promising. 


ARO AND AGS RADARS USING LIGHTHOUSE TUBES 


81 


Work on the AN/APG-3 began at the end of 
1943, and the system was given ground tests in 
the summer of 1944. Sperry was given a contract 
for a similar system, the AN/APG-16, and pro- 
duction on both these systems was pushed in 
1945. These systems represented an attempt to 
produce a more practicable AGL than the heavy 
(400-500 lb) systems previously developed, and 
was part of the intensive program to provide 
every conceivable form of radar for the B-29. 

6.7.3 Field Application of AGL 

The AGL program suffered undoubtedly from 
the fact that, having been conceived very early, 
the systems that emerged were modifications of 
a fairly primitive form of microwave radar. The 
sets were heavy in consequence, and therefore 
were unpopular with the Army forces. There 
was never much enthusiasm within MIT-RL, 
even in Division 9, which at one time tried to 
have them transferred to Division 8. 

It must be kept in mind, however, that tactical 
considerations, changing with the course of the 
war, had an enormous influence on the amount 
of emphasis placed upon this as well as other 
airborne programs. When AGL was first con- 
ceived it was expected that bombers might fly 
solitary missions or in loose formation, often at 
night, and that protection against enemy fight- 
ers, especially nightfighters, would be urgently 
needed. As far as heavy bombardment aircraft 
were concerned this was never the case. The 
doctrine of daytime, tight-formation flying 
which had been adopted reduced the importance 
of the AGL type of equipment. Although, until 
the last stages of the offensive against Germany 
and against Japan, fighter opposition was often 
serious, it never threatened to cripple the air 
offensive, which would have meant greater con- 
cern for bomber defenses. 

6.8 AIRBORNE RANGE-ONLY [ARO] AND 
AIRBORNE GUNSIGHT [AGS] RADARS USING 
LIGHTHOUSE TUBES 

Initiation of ARO Project 

The lighthouse tube transmitter-receiver 
[LHTR] systems, designated variously as ARO, 
AGS, Falcon, TW, and their modifications, all 
were designed around the same standard unit. 


This is a lightweight, pressure-tight unit con- 
taining a transmitter-receiver, with lighthouse 
tubes, and a power supply. The LHTR Mark I 
was developed by H. L. Schultz in 1942 in the 
course of his work on ARO. A lighter, smaller 
unit, the LHTR Mark II, was developed in 1943 
for use with another system, but was never put 
into production. The first LHTR operated at 10.7 
cm ; in 1943 the band 11.0 to 12.5 cm was officially 
assigned for LHTR operation. The LHTR unit 
is used in all its applications without internal 
modification, though various improvements have 
been incorporated since 1942. 

Airborne range-only [ARO] was formulated 
as a project in April 1942 following a request 
from the Bureau of Ordnance. The U. S. Navy 
had been interested since January 1942 in a sys- 
tem to be combined with the Ford Instrument 
Company’s fire-control system, but the idea was 
not then practicable. The U. S. Army became 
interested in June 1942 and most of the subse- 
quent development was done for the AAF. 

Development of ARO Equipment 

Requirements. Range for the fire-control 
mechanisms then in use was supplied by rather 
crude stadiametric measurement. ARO was to 
supply range automatically, with no attention 
from the gunner. The necessary components 
were developed in the spring and summer of 
1942. These were an LHTR and a range unit, 
both light and compact, to be used with an 8-in. 
paraboloid. RCC agreed to build 10 LHTR’s and 
6 range units, and the Philco Radio Corporation 
and the Galvin Manufacturing Company re- 
ceived small educational orders. Production was 
delayed by the great difficulty experienced in 
obtaining lighthouse tubes. 

Testing. During the fall of 1942 the labora- 
tory-built ARO was given flight tests in a B-18. 
In January the system, in which a polystyrene 
rod antenna (end-fire array) was substituted 
for the paraboloid, was sent to Wright Field for 
tests in a B-17. After successful firing tests with 
improved units at Eglin Field, Florida, the U. S. 
Army ordered 400 sets (designated AN/APG-5) 
from Galvin. Meanwhile the Navy was conduct- 
ing exhaustive tests at Norfolk, Virginia. The 
Army laid out a series of future tests including 
the installation of ARO in a B-25G for use with 
75-mm cannon (this was the start of Falcon) 


82 


AIRCRAFT RADAR SYSTEMS 


and firing tests of ARO in the Emerson lower 
ball turret of a B-17 ; possible installation in 
B-29’s was also considered. 

Production and Application. RCC production 
began in June 1943. Galvin produced their first 
6 (preproduction) systems in April 1944. Since 
there was little chance of quantity production 
in 1944, the U. S. Army agreed to cancel all 
orders except for the 25 preproduction systems, 
and the U. S. Navy requirement was reduced to 
80 sets. A large part of the delay was caused by 
engineering difficulties arising from the auto- 
matic features of the system. There were also 
conflicts with other, more urgently needed, 
LHTR systems. After various modifications to 
permit the use of ARO with the K-15A gunsight, 
Galvin resumed production in May 1945. 

In January 1944 plans were made to install 
ARO in B-29’s. One installation (called AN/APG- 
14) was made in August 1944 as part of Project 
Wasp. A more important ARO project was Fi- 
garo. This was the installation of ARO in B-17’s, 
and, later, B-24’s, first discussed in the spring of 
1944. Five B-17’s arrived at Bedford in October 
of that year; by December they were on their 
way to the Fifteenth Air Force in Italy, followed 
by 5 B-24’s in May 1945. These installations were 
successfully flown on many missions, but no 
tactical experience was gained for no enemy op- 
position was encountered. 

® ^ ^ Initiation of AGS Project 

AGS Mark I Model 

Work on an airborne gunsight [AGS] was be- 
gun November 1, 1942, with J. V. Holdam as 
project engineer. Somewhat earlier the labora- 
tory had received requests from the Army for 
such a project. It was decided to develop first, a 
lightweight system based on ARO, without a 
computer, for installation in the Emerson tail 
turrets of B-24’s, and second, as a long-range 
project, a system for use with lead computing 
sights. The necessary modifications included the 
addition of conical scan, the precise coordination 
of the radar axis of scan with either the bore- 
sight line or the sight line, and the addition of 
an indicator unit. The indicator presentation 
was a spot the position of which was an indica- 
tion of target bearing, and on which grew wings 
whose size varied inversely with the range. 


Since there was some doubt of the adaptability 
of the LHTR to such a system, an alternate devel- 
opment of a low-voltage magnetron transmitter- 
receiver, the SMTR, was initiated. This, known 
as the AN/APG-10, was cancelled in November 

1943. 

By April 1943 a complete system, with an end- 
fire array antenna, was undergoing flight tests 
in an AT-11. In July an AGS Mark I was flight 
tested in the Emerson tail turret of a B-24. An 
NDRC contract for 25 AGS Mark I systems was 
given to Galvin to provide models for experiment 
and possible operational trial. 

AGS Mark II Model 

Development continued on various AGS sys- 
tems and by October 1943 there were several rec- 
ognized versions. The AGS Mark I ( AN/APG-8) 
had no computer and was designed for installa- 
tion in an Emerson tail turret. The AGS Mark 
II (AN/APG-8B or AN/APG-15) was the 
AN/APG-8 modified for installation in the tail 
of a B-29. The AGS-2 Mark II was the low-volt- 
age magnetron version of the AN/APG-15, and 
the AGS-3 Mark I was an LHTR system for 
installation in an Emerson tail turret in conjunc- 
tion with the Fairchild lead computing sight. 
The Army, encouraged by preliminary tests, set 
up a requirement of 3,500 sets in 1944, with con- 
tracts let to the General Electric Company and 
to Galvin Manufacturing Company. In May 

1944, however. Falcon was given precedence 
over other LHTR systems, and AGS contracts 
were curtailed. 

Development of AN/APG-15 

At MIT-RL intensive work was being done on 
the problem of boresighting in an effort to de- 
velop satisfactory techniques for factory and 
field. In August 1944 the Army requested assist- 
ance from the laboratory for Project Wasp, a 
crash program to install AN/APG-15 in seven 
B-29’s and AN/APG-14 in one B-29. Work was 
begun in November and completed on schedule 
in the same month. The result of this program 
was the development of the AN/APG-15B. This 
provides automatic radar range to the computer 
for visual tracking, while at night it gives tail 
warning and point-blank bearing information. 
Five of these B-29’s were sent to the 58th wing. 
Twentieth Air Force, in India for combat test- 


FALCON, VULTURE, AND PTERODACTYL 


83 


ing. The systems operated successfully, but little 
tactical information was obtained. 

By February 1, 1945, GE had produced 272 
AN/APG-15A’s; thereafter only AN/APG- 
15B’s were accepted. The total production was 
9,376. Both the 315th and 316th wings of the 
Twentieth Air Force were equipped with 
AN/APG-15. Operation was fairly satisfactory, 
but little tactical information was ever obtained 
since there was little enemy fighter opposition. 

6.9 FALCON (AN/APG-13A) , VULTURE 
(AN/APG-13B), AND PTERODACTYL 
(AN/APG-21) 

Development of Falcon 
Requirements 

After successful tests of ARO in the spring 
of 1943 it was decided to test the system in a 
B-25G with 75-mm cannon. Such an aircraft has 
a fixed gunsight mounted parallel to the cannon 
boresight axis ; the pilot aims the cannon by fly- 
ing the plane so that the sight is lined up with 
the target. Accurate range determination is 
necessary. 

Adaptation of ARO to Falcon 

ARO in a B-25G was tested in September, and 
MIT-RL began to modify the basic ARO com- 
ponents. This involved elimination of the auto- 
matic range unit, range servo, and calibrator, 
which were replaced by an M-scope, and the ad- 
dition of a ballistic cam to make the rotation of 
the range adjusting shaft linear with range. The 
radar operator adjusts a hand crank to keep an 
electronic marker in coincidence with the target 
signal; this provides range adjustment of the 
gunsight through a flexible shaft. In December 
1943, a laboratory system was ready for tests at 
Eglin Field and RCC had under way the produc- 
tion of 30 systems for a special experimental 
squadron. In April 1944 the first RCC order was 
complete, and the Army asked for 120 more sys- 
tems. At the same time an order was given for 
880 sets to be built on a crash basis, the M-scopes 
at the General Electric Co. and the LHTR units 
and antennas at Galvin Manufacturing Company. 

By June 1944 the first experimental squadron 
was in action with the Fifth Bomber Command 


in New Guinea. The equipment performed well, 
though ship targets were already scarce. By fall 
the Fourteenth Air Force was using Falcon with 
great success. Operational experience showed 
the necessity of a device to permit setting in 
actual airspeed, since in combat varying speeds 
were used. The laboratory provided such an at- 
tachment. 

Development of Falcon 

During the summer of 1944 the Army asked 
for a unit to permit mechanical instead of hand 
tracking, and it became obvious that a modifica- 
tion of Falcon for use over land was required. 
This was the start of Overland Falcon or Vul- 
ture. The Vulture presentation, in which all tar- 
gets in the radar beam appear on the indicator, 
but with the target signal clearly differentiated, 
was proposed by E. H. B. Bartelink in May 1944. 
Falcon can be readily converted to Vulture by 
the addition of a subpanel to the M-scope, the 
replacement of the antenna by an AGS scanner, 
and the addition of an aided tracking unit to 
replace the hand crank which feeds range in- 
formation to the gunsight. 

The laboratory built model was successfully 
flown in November 1944. In February 1945 Gen- 
eral Chennault requested 30 modification kits to 
convert Falcon to Vulture; his Fourteenth Air 
Force had used Falcon with great success but 
they had been pushed back in China and needed 
an overland system. RCC undertook a crash pro- 
gram which was completed in August. During 
the spring and summer of 1945 a good deal of 
thought was given to the problem of adapting 
Falcon or Vulture for rocket firing. The Applied 
Mathematics Group at Columbia gave a good 
deal of help on the problem of designing the 
necessary computer and ballistic cams. 

Development of Pterodactyl 
By the beginning of November 1944 Auto- 
matic Vulture or Pterodactyl was ready for 
flight tests. This was an automatic system which 
searched in range, and only locked on a target 
when both range and directional information 
was correct. In June 1945 work began at the 
laboratory on assembling 5 systems from the 
improved ARO components then in production. 
RCC had an order for 12 units which were com- 
pleted in October 1945. 


84 


AIRCRAFT RADAR SYSTEMS 


6.10 LOW-VOLTAGE MAGNETRON 
SYSTEMS, AN/ APS-10 

Experimental Work 

The low-voltage magnetron systems are close- 
ly allied with the lighthouse-tube systems. Both 
types of transmitters draw only a small amount 
of power and hence are more suitable for the 
design of lightweight radar sets where range is 
not the principal consideration. Development of 
experimental low-voltage magnetron systems 
had proceeded far enough by the beginning of 
1943 so they could be conceived of as possible al- 
ternates for the LHTR systems. Work was also 
done on a low-voltage magnetron tail-warning 
system, the AS J. The only low-voltage magnetron 
system that was pushed beyond the initial stages 
of development was the AN/' APS-10, also known 
as blind-flying radar [BFR] . This was derived 
from the LWASV, a lightweight LHTR system 
begun in November 1942 and terminated in June 
1943, since it did not meet the U. S. Army re- 
quirements for weight and performance. 

6 . 10.2 Development of AN APS-10 
Experimental Objectives 

At the time the LWASV project was termi- 
nated the U. S. Army expressed an interest in a 
very lightweight ASV, to be called the AN/APS- 
10, which would be simple and reliable, with 
relatively short range, suitable for use with 
beacons and IFF. During the summer of 1943 
work was started by H. L. Schultz on the XMTR, 
a 3-cm, low-voltage magnetron transmitter- 
receiver. As development proceeded it appeared 
that the system based on XMTR would be even 
more useful as a navigational device than as an 
ASV system. The need for such a navigational 
aid was strongly urged upon the laboratory by 
Colonel Stuart P. Wright on his return from the 
Wright project mission to the South Pacific. 

Design Characteristics 

By the beginning of 1944 the first laboratory 
model was fiying successfully. This had an 18-in. 
CSC- antenna, the XMTR unit, but only a make- 
shift indicator. Various improvements were 
made and at an Army-Navy meeting on Febru- 


ary 25, 1944, the Army decided that the AN/APS- 
10, based on the XMTR, would definitely meet its 
requirements for a lightweight, simple naviga- 
tional device for use on transport planes. Several 
engineers from GE, the chosen manufacturer, 
had already arrived at the laboratory to work 
with the system, and on March 22 there was a 
meeting at which the AN/ APS-10 program was 
set up. The laboratory agreed to act as consult- 
ant, with A. Longacre as project engineer for 
production, while R. L. Sinsheimer remained 
project engineer for the work at the laboratory. 
In the succeeding months details of the system 
were thoroughly worked out. It was designed 
above all to be reliable, rugged, simple to operate, 
and easy to service. The number of controls were 
sharply limited, so that reliable automatic tun- 
ing was imperative ; for easy servicing the vari- 
ous units were designed to be replaceable and 
completely interchangeable. 

Production and Field Application 

The GE engineers remained at MIT-RL until 
the summer of 1944. By the time they left 
the engineering drawings were complete. The 
laboratory built three prototype systems based 
on these drawings, one of which served as the 
GE prototype, while the others were used for 
tests. A new and improved scanner was designed 
and manufactured by the Houston Corporation 
at the instigation of RL. Two hundred of these 
were purchased by the Army through GE as 
extra equipment. At the beginning of 1945 the 
system was demonstrated to Troop Carrier Com- 
mand [TCC], which was very enthusiastic. A 
30-in. scanner was developed for TCC, to give 
improved resolution for navigation. 

Production at GE was slow, due largely to 
procurement difficulties and necessary design 
changes. The 50 preproduction systems were 
completed by April 1, 1945. Since GE had sub- 
contracted the manufacture of components, 
though still assembling and testing the sets, 
quantity production was delayed until June. By 
August, 300 sets a month were being produced. 
Such sets as were available before the end of the 
war were installed in C-46 transport planes for 
the TCC. It is reported that C-46's with the 
APS-10 were in Japan in September 1945. 


Chapter 7 


SHIP SYSTEMS 


7.1 SHIP CONTROL OF INTERCEPTION^ 
Development Program 

A S POINTED OUT in Section 2.2, the earliest pro- 
^duction shipboard system available to the 
U. S. Navy was the CXAM, an aircraft warning 
system operating at 200 me per sec, the first unit 
of which was delivered in May of 1940. This set 
suffered from the defects characteristic of low 
frequency, and its usefulness was impaired by 
its lack of height-finding features. 

Requirements 

The control of the interception of enemy planes 
from an aircraft carrier requires accurate in- 
formation on the altitude as well as azimuth and 
range of the approaching craft. The cooperation 
of Division 14 in the Navy program for the de- 
velopment of such radar dates from December 
8, 1941, when the Navy, in Project NS-101, pro- 
posed the development and construction by 
NDRC of a model radar that would be capable 
of the accurate determination of the altitude of 
approaching bombers. As a result the completed 
experimental set designated CXBL was installed 
in the carrier Lexington in March 1943 as stated 
in Section 5.1. This was the first height-finding 
set on an American aircraft carrier. 

SM AND SP Systems 

The first SM production model of the CXBL 
was installed on the carrier Bunker Hill in Sep- 
tember 1943. The SP, a lightweight version of 
the SM, was to go into production nine months 
later than the SM. These sets required that the 
radar-controller point the antenna at only one 
plane at a time in order to determine its height, 
a factor that seriously limited the traffic han- 
dling capacity of the system and simultaneously 
prevented this powerful microwave system from 
being used for low coverage. 

SCI OR eXHR System 

Requirements. On August 18, 1943 the radar 
design section of the Bureau of Ships [Bu- 

» This section was prepared by J. S. Hall, project engi- 
neer SCI. 


Ships] requested MIT-RL to develop a radar 
that would give the height of all aircraft within 
50 miles every 15 seconds and at the same time 
provide high- and low-microwave coverage. The 
desired coverage was to be 80 miles on all air- 
craft below 40,000 feet and below an elevation 
angle of 20°. Since the antenna weight was an 
important design limitation it was planned to 
place the antennas for both the height-finder 
and the search system on the same stabilized 
mount. 

Operational Characteristics. A Robinson 
scanner was selected as the feed for the height- 
finder. At 8.5 cm the Beavertail beam of the 
height-finder was 3.5° wide and 1.1° high. This 
beam scans from the horizon to an elevation of 
11°, 600 times per minute. At the same time the 
mount rotates in azimuth and height data is con- 
tinuously presented on RHI’s at the several con- 
soles. As the mount rotates at 4 rpm the height 
beam hits the target 3% sec later than does the 
search beam. The search beam is 1.7° wide in 
the horizontal direction and is fanned up to 18° 
vertically. 

All the information presented by these two 
radar systems on the same mount is presented 
at any one of the five mutually independent con- 
soles. Each console has a PPI, an off-centered 
PPI, and an RHI. The width of the azimuth sec- 
tor where signals may appear on the RHI is ad- 
justable. The coordination of the three scopes 
on each console, the use of five independent con- 
soles for each equipment, and the ability of this 
system to provide height data under conditions 
of continuous scan are reasons for its greatly 
superior traffic handling capacity, when com- 
pared to SM or SP. 

Design Problems. The most difficult problem 
connected with this type of system was that of 
designing the Robinson feed. An experimental 
system involving only the height-finder was put 
into operation early in March 1944 on the roof 
of Building 6 at MIT. This system had a range 
of 45 nautical miles on a two-motored plane 
(SNB). Its height accuracy was satisfactory 


85 


86 


SHIP SYSTEMS 


and its coverage to 11° elevation angle was ade- 
quate. In April 1944 it was decided that the two 
prototype sets (later designated CXHR by the 
Navy) should be built. The General Electric 
Company [GE] agreed to build most of the com- 
ponents for these two sets and to deliver them by 
January 1, 1945. The MIT-RL was to design and 
build the two main control panels and the two 
r-f heads. These r-f heads were to be placed be- 
tween the reflectors on the mount. 

Experimental Installation 

A building with a radome on top of it was con- 
structed at the Spraycliff Field Station located 
at Beavertail Point, Jamestown, Rhode Island, 
which would house both the equipment and the 
mount. During April, May, and June the height- 
finder was moved from the roof of Building 6, 
and, together with an early warning dish, was 
placed on a United Shoe Machinery mount. This 
mount was installed in the radome at Spraycliff. 
The experimental set-up was designated SCI and 
was heavily depended upon as the radar used to 
direct flyers in night interceptions in the night- 
fighter training program at Beavertail. Many 
such flyers later saw action in the Pacific. 

Flight Test Results 

Beginning in January of 1945 W. 0. Gordy 
had taken over the responsibility of carrying out 
experimental flight tests with the experimental 
search system at Fisher's Island. Flight tests 
were run throughout this year and work was 
conducted in close cooperation with the antenna 
group at Ipswich. The early experiments showed 
a considerable amount of reflection from the 
water and the resulting peaks and nulls gave 
spotty coverage. This was ascribed to the fact 
that the energy was horizontally polarized. A 
vertically polarized antenna with a 5-ft by 14-ft 
dish and a three-horn feed was then constructed. 
Gordy obtained results which, while not quite as 
good as requested by the Navy, seemed adequate. 
He found that a two-motored plane could be fol- 
lowed consistently to 80 nautical miles up to alti- 
tudes of 20,000 ft and in to elevation angles of 
15 to 18 degrees. He then returned to the labora- 
tory in December 1944 and issued a report, RL- 
703, describing this work. The complete SCI 
system was demonstrated to the Navy in July 
1944 at Spraycliff. 


Director Console Design 

During May, G. W. Fyler of GE, who was orig- 
inally scheduled to produce the SCI consoles, 
conceived the idea of building a “soda fountain" 
console around which all fighter-director officers 
would sit and obtain their data from a single 
skiatron. In the meantime MIT-RL had built two 
experimental consoles. The Navy was anxious to 
see both types tried out and consequently NDRC 
authorized Fyler to build the type which he had 
suggested and to place it in competition with 
MIT-RL consoles at Spraycliff on July 1. The 
Navy decided in July that the type developed by 
MIT-RL where each fighter-director officer was 
at a different console separated from the others 
was the better solution. Fyler then agreed to 
build eight consoles according to MIT-RL speci- 
fications. 

7.1.2 Production and Training Program 
(CHXR and SX Systems) 

In the fall of 1944 the Navy ordered four pro- 
duction systems designated SX from GE. De- 
livery was to start in July 1945. Early in Sep- 
tember a number of GE engineers came to MIT- 
RL and worked during September, October, No- 
vember, December, and part of January design- 
ing parts of the SX system. During this same 
time and the early months of 1945 the laboratory 
built the two main control panels and r-f heads. 

Eighteen officers and men spent about eight 
weeks at MIT-RL during May and June 1945 in 
an intensive training program. The RL training 
group under H. H. Wheaton had charge of this 
training program. 

The first CHXR system was tried on the roof 
of MIT Building 20 in May 1945. Subsequent 
flight tests showed that the height system had a 
range approximately ten miles greater than that 
which had been obtained a year previously on the 
roof of Building 6. This improvement was the 
direct result of an improved Robinson feed. The 
early-warning system had the same coverage and 
was about equally solid as that which Gordy re- 
ported in RL-703. 

BuShips ordered 41 SX systems from GE on 
February 24, 1945, with delivery of these sys- 
tems to start in March 1946. 

In June the second CHXR system was in- 
stalled at a U. S. Naval Air Station on St. Simon 


GUN FIRE-CONTROL SYSTEM MARK 56 


87 


Island, Georgia. The system on the roof of Build- 
ing 20 was shipped and installed on the carrier 
Midway in July 1945. The first production SX 
was installed on the carrier Franklin D. Roose- 
velt in August 1945. The performance of each of 
these systems was similar to that found on the 
roof of Building 20 as regards the height-finder. 
However, the early-warning of system seemed to 
have gaps in its coverage of 8° or 9° elevation 
angles. These gaps were serious and still need to 
be thoroughly investigated. The range, however, 
on the search part of these three systems was 
found to be somewhat greater than had been an- 
ticipated. This fact suggests that some of the en- 
ergy which was to be radiated at 8° or 9° is going 
into the main horn. Since similar problems have 
been solved in other radars, this difficulty can 
undoubtedly be remedied. 


7.2 gun fire-control system mark 56 

^ Origin of Mark 56 

The gun fire-control system Mark 56, of which 
the radar Mark 35 is an integral part, is an out- 
growth of the automatic tracking developed in 
XT-1 and the SCR-584. It is an attempt to arrive 
at a balanced integration of radar and computer 
into a director system functioning as a unit and 
represents a break with the policy of trying to 
adapt radar sets to gun directors designed before 
the advent of radar or planned without radar as 
the primary source of data. The Mark 56 is an 
intermediate-range director to control Navy 
.38-cal, 5-in. AA guns. 

The Bureau of Ordnance [BuOrd] request for 
the Mark 56 grew out of conversations between 
I. A. Getting and H. L. Hazen with Captain Mur- 
phy in the summer of 1942. Captain Murphy was 
pleased with Getting’s suggestion that MIT-RL 
would like to undertake an integrated job for the 
Navy. Further conversations with Lieutenant 
Commander Irven Travis, in charge of the AA 
Direction Sub-Section (Re4c), brought out the 
information that BuOrd would like NDRC to 
carry the project through to prototype design. 
The project was requested and endorsed by the 
Navy’s coordinator of research and development 
on May 19, 1943, and was assigned jointly to 
Divisions 14 and 7 of NDRC, although Division 


14 was given administrative responsibility for 
contract work. 

The project was coordinated at MIT-RL by 
1. A. Getting, and H. A. Kirkpatrick was ap- 
pointed project engineer, assisted by R. P. Scott, 
for gun director Mark 56, and H. S. Sommers for 
the radar Mark 35. 

Mark 56 Systems 

Function and Operation 

Functionally the gun fire-control system Mark 
56 is divided into three systems : (1) radar Mark 
35 which has the functions of locating and track- 
ing the target and of supplying position and rate 
data to the computer, (2) the director proper, 
whose function is to furnish present position 
data to the computer plus target angular rates 
in a stabilized system, and (3) the computer 
which supplies accurate gun orders and fuze 
time. 

The Mark 35, operating on 3 cm, is the first 
radar to combine fixed polarization with conical 
scanning and automatic tracking. Fixed polar- 
ization gives freedom from Window and other 
kinds of jamming. Spiral scan (wide beam) is 
used for target acquisition. When the target is 
picked up, the operator switches to automatic 
tracking and conical scan (narrow beam). A 
nutating antenna keeps*the plane of polarization 
always vertical. The range system, with its very 
narrow gate, permits tracking of an aircraft 
when it is separated from another by as little 
as 25 yd in range (the improved range gate on 
SCR-584 was 60 yd long) . 

The director makes use of a processing line- 
of-sight gyro and computer, designed by MIT- 
RL, which together with a vertical gyro and 
stable vertical (adapted from a vertical designed 
by GE ) keep the system on an even keel so that 
tracking information is always given in stable 
coordinates. 

Production and Application 

Getting and others from MIT-RL attended 
a meeting at GE, on December 30, 1943, to 
discuss details of the OSRD contract which GE 
had agreed to accept for the development of com- 
ponents and the eventual construction of two 
prototype models of the Mark 56 system. From 
this time on there was an exchange of informa- 


88 


SHIP SYSTEMS 


tion between GE and RL and a division of re- 
sponsibilities for the development of the model, 
Mark 56X, set up by the laboratory at its Heath- 
field Station at Fort Heath, and also an experi- 
mental model at Schenectady. The laboratory 
built two other experimental models, Mark 56 A 
and Mark 56B. 

The first radar signals on Mark 56X were ob- 


tained on December 28, 1944. From this time 
until the end of the war tests were run at Heath- 
field. The complete system Mark 56 Model A was 
set up at Heathfield Awhile Model B, without the 
ballistic computer, was installed aboard the 
destroyer USS Winsloiv in December 1945. In 
the fall of 1945, the U. S. Navy placed a produc- 
tion order with GE. 


Chapter 8 


PROJECT CADILLAC, AIRBORNE EARLY-WARNING RADAR SYSTEMS 


8.1 INTRODUCTION 

T he project which absorbed the largest por- 
tion of MIT-RL’s attention and effort in the 
last year of the war was the development of a 
highly complex mass of equipment first referred 
to as airborne early ^earning [AEW] and later 
for security reasons called “Projectile Cadillac,” 
after Maine’s Mount Cadillac on the peak of which 
an experimental version of the equipment was 
tested for several months. Cadillac was Ameri- 
ca’s most urgent radar project in the several 
months before the end of the war ; it can fairly 
be described, also, as the most complex electronic 
undertaking of the war from an administrative 
as well as a technical standpoint. The organiza- 
tion and conduct of this program, involving the 
close cooperation of many separate groups, with 
MIT-RL serving as the principal coordinating 
agency, is a wartime research and development 
story well worth careful study. 

8.1.1 Purpose of Project Cadillac 

The purpose of Project Cadillac was to over- 
come the chief weakness of shipboard search 
radar, namely, its inability to see beyond the 
horizon. The Japanese fully exploited this hori- 
zon limitation, coming in on our ships as low 
over the water as possible. In 1944 this technique 
was used in their effective Kamikaze attacks ; a 
variety of tactics was used in making the at- 
tacks, but in particular the Japanese found they 
could circumvent the radar defenses of the fleet 
by making their final attacks from the zenith 
where there was no radar coverage, or close to 
the surface below the beams of the long wave 
search radar of the ships. The best defense for 
all tactics was to pick up the planes at as great 
a distance as possible as they approached the 
task force. The Kamikaze attack made the exten- 
sion of the fleet’s radar warning range a top 
priority Navy problem just when the emphasis 
in the American war effort shifted from Europe 
to the Pacific. 

The Cadillac equipment could also serve an 
important role (increasingly so as our forces in 


the Pacific grew in numbers and complexity) in 
coordinating task force and amphibious opera- 
tions. For example, in such an operation as the 
invasion of Japan, when vast armadas of ships 
and planes would have to be used, the airborne 
relay radar system could provide all CIC simul- 
taneously with comprehensive data on the dis- 
position of both friendly and enemy ships or 
aircraft over a wide area. 

8.1.2 Origin of Project Cadillac 

The airborne-relay radar, which was the key 
device for realizing the Project Cadillac idea, 
grew out of an earlier MIT-RL development. In 
J une 1942 the Committee on Joint New Weapons 
and Equipment had suggested developing a relay 
link to extend the range of a radar set. Soon after 
the Navy requested the laboratory to investigate 
the possibilities of such equipment and to de- 
velop a unit for a Service test. A television trans- 
mitter-receiver, loaned to the laboratory for two 
weeks by RCA, was set up in Building 24. On 
August 14, 1942, transmission on a radio link 
between Building 24 and an experimental radar 
system on the roof of Building 6 was successfully 
demonstrated. 

Development of AN/APS -14 

Difficulties encountered in these tests led to 
the decision to substitute frequency modulation 
for amplitude modulation. In September an ex- 
perimental FM television transmitter was 
loaned by Zenith Radio Corporation, and in the 
following months successful FM transmission 
between the two buildings on the campus was 
obtained. Plans were then made for transmis- 
sion from aircraft. A 100-mc receiver was de- 
signed and built. By May 1943 satisfactory PPI 
reproduction had been received at the East Bos- 
ton Airport through relay radar in an airplane 
flying over the island of Nantucket at 10,000 
feet. 

At this time the radio link was reliable for 
about 50 miles. Shortly thereafter, in July 1943, 
the relay radar (AN/APS-14) was demon- 


89 


90 


PROJECT CADILLAC, AEW RADAR SYSTEMS 


strated to naval officers at the East Boston Air- 
port; a short film illustrating the system was 
prepared for COMINCH, which resulted in a 
request that the reliable range be extended to 
100 miles or more. This was done.» 

8.1.4 Organization of Project Cadillac [AEW] 

Since subsequent production had not been de- 
cided upon at the end of December 1943, Division 
14 asked that the relay-radar project be termi- 
nated. A month later, however, the U. S. Navy 
proposed a project to develop an airhorne early- 
warning [AEW] system, incorporating a high- 
powered relay-radar device. The AEW project 
was then developed under RL code name of 
Project Cadillac. 

The basic idea for Cadillac (extending the 
ship search antenna into the air) was simple 
enough. Achieving a workable system, however, 
was one of the most complex and difficult de- 
velopmental problems attacked by the labora- 
tory. The project was not only the largest in the 
history of the laboratory, but was of a new order 
of magnitude. In addition to engineering the com- 
plicated airborne system, an equally complicated 
shipboard system was required. So too was iden- 
tification (IFF) equipment, test equipment, and 
a suitable voice communication system. In short, 
several types of electronic equipment, integrated 
into a system, were needed in the shortest pos- 
sible time. 

The Cadillac Project was first proposed in 
February 1944. After a series of conferences be- 
tween representatives of BuOrd and MIT-RL, 
the U. S. Navy in April 1944 formally requested 
the NDRC to establish the project. In March 
1945, just thirteen months after the first request, 
the first production system was delivered to the 
Navy. 

The Cadillac production achievement was 
made possible, of course, by the scale of the co- 
operative effort. A large proportion of the mem- 
bers of nine of the laboratory’s eleven divisions 
worked on the problem. The Bureau of Aero- 
nautics, the Bureau of Ships, the Naval Aircraft 
Modification Center at Philadelphia, the Naval 
Research Laboratory, several Navy contractors, 

aThe National Broadcasting Company collaborated 
with MIT-RL in the early relay-radar development un- 
der an OSRD contract negotiated with RCA. 


and a number of Radiation Laboratory subcon- 
tractors all contributed substantially to the 
equipment as it finally evolved. The scope of 
Project Cadillac at the laboratory is indicated by 
the fact that direct outside purchases for the 
project (not including large stockroom with- 
drawals) constituted 12 per cent of the total 
expenditures of the laboratory for materials and 
services for the entire five years of its existence. 
At the peak of the program, during the summer 
of 1945, approximately 20 per cent of the time of 
all the laboratory’s technical staff members 
working on specific projects was spent on Cadil- 
lac. Navy personnel at the laboratory who were 
an integral part of the laboratory program 
reached a total of 160 officers and men. 


8.2 AEW CADILLAC I SYSTEM 

System Components 

The AEW Cadillac I system as it reached the 
fleet was in two basically separate sections : an 
airborne section, carried in a modified torpedo 
bomber, and a shipboard section for the pre- 
sentation in visual form of the information re- 
layed from the airplane. The complexity of both 
these sections was an outstanding aspect of the 
project. 

Airborne System 

The airplane, a TBM-3, was redesigned to 
carry the estimated 2,300 lb of equipment. The 
Naval Aircraft Modification Center [NAMC] 
undertook to adapt the plane and to conduct the 
necessary wind tunnel and flight tests. An 8-ft 
diameter bulbous radome was mounted between 
the aircraft’s wheels to house the radar antenna. 
The ball turret, armor and armament, including 
the torpedo bay, were removed. Two additional 
tail stabilizers, a high-power supply operated by 
the engine, substantial modifications to the in- 
terior of the plane, and the mounting of nine 
different antennas at various locations on the 
wings, tail, and fuselage completed the plane 
modifications. 

Radar Equipment. The radar equipment, 
AN/APS-20, operated at 10 cm with a peak 
power output of 1 megawatt and a 2-/xsec pulse. 
The heart of the airborne section was a complex 


AEW CADILLAC I SYSTEM 


91 


synchronizer and a radar receiver with many 
new features. The airborne section also included 
the IFF interrogator-response, AN/APX-13. 
This was designed with the highest available 
peak power (2 kw) and most sensitive receiver 
in any airborne IFF development, to make pos- 
sible the identification of targets on both of 
the standard Navy A and G bands at ranges 
comparable to the detection ranges of the 
radar equipment. The relay-radar transmitter, 
AN/ART-22, which was based upon the earlier 
laboratory project, broadcast, on any of several 
channels around 300 me as selected, both radar 
and IFF information for reception by the ship- 
board section. Both the IFF and relay equipment 
were synchronized by the radar synchronizer, 
which also coded their outputs prior to relaying 
so as to ‘‘get through” interference or enemy 
jamming. A modified fiux gate compass used to 
orient the radar information, a new type radio- 
control receiver (AN/ARW-35) making pos- 
sible control of functions of the airborne equip- 
ment from the shipboard section, a relay system 
(AN/ARC-18) for relaying voice communica- 
tion between ships and planes or other ships over 
the horizon, and the standard IFF transponder, 
voice communication equipment, radio alti- 
meter, and homing receiver completed the air- 
borne electronic gear. 

Shipboard System 

Any ship equipped with the shipboard section 
of AEW could, if within relay range, receive and 
display the information relayed from a plane. 
The shipboard section of AEW was also com- 
posed of several different devices, depending 
upon the requirements of the particular installa- 
tion. The relay receiving equipment used either 
an omnidirectional or a horizontal diversity re- 
ceiving system to pick up the information broad- 
cast by the relay transmitter in the plane. Ad- 
justable band-pass tuning cavities in the antenna 
line, and line filters for all other shipboard sys- 
tems which transmitted side band energy on the 
relay frequency, were developed to minimize 
interference with the relay reception. The relay 
information, after it had been decoded by the 
complex and precision-adjusted decoder, was 
piped to two, three, or more PPFs located usually 
in the ship’s combat information center [CIC] . 


Coordination of Airborne and 
Shipboard Systems 

The picture on each indicating scope could be 
expanded in various ways. Facilities were de- 
vised so that the AEW airplane’s motion could 
be eliminated and the picture centered on the 
receiving ship. Another innovation of the indi- 
cating system was the delayed PPI (also avail- 
able in the plane) by which any 20-mile region 
of the main PPI picture could be expanded for 
detailed examination over the complete face of 
the tube. 

A transponder beacon (YQ) of the Black 
Maria type responded in code on the IFF G band 
to interrogation from the plane, making possible 
identification of the receiving ship in the midst 
of other shipping. Interrogation could be radio- 
controlled from the ship and was accomplished 
by the coincident reception of 10-cm radiation 
from the airborne radar and G-band reception 
from the airborne IFF transmitter; or, if so 
desired, by coincident reception of the 10-cm 
radiation and a trigger signal transmitted over 
the radar relay link. A radio control-transmitter 
(AN/ARW-34) and standard voice communica- 
tion equipment completed the shipboard elec- 
tronic equipment. 

Development of Cadillac I 

Experimental Systems 

To speed the development of a coordinated 
system, a ground radar set which simulated at 
lower power the projected AEW radar perform- 
ance was established on Mount Cadillac, near 
Bar Harbor, Maine, where it operated for sev- 
eral months. Five complete air and ship AEW 
experimental systems were planned and con- 
structed. The first airborne section was com- 
pleted and flown in August 1944. The other four 
airborne sections, each improved somewhat over 
the one preceding it, followed at intervals of 
about a month. Shipboard sections were com- 
pleted at the same rate, though started approxi- 
mately one month later. 

Organization. The AEW organization began 
in rather modest terms. W. P. Dyke, earlier the 
project engineer for ASG and ASD-1, was put 
in charge. Somewhat independent investigations 
of various aspects of the system were initiated 
in the transmitter division and receiver division 


t SECRF,1’~9 


92 


PROJECT CADILLAC, AEW RADAR SYSTEMS 


groups concerned. However, by May 1944, when 
acceptance of the project was recommended to 
NDRC by Division 14, a complete group organ- 
ization was established in the laboratory. 

Demonstration of AEW System. In October 
1944 the first full-scale demonstration of the 
AEW system was given to a large group of Navy 
and Army leaders. For two weeks preceding the 
demonstration, two eight-hour shifts of person- 
nel operated at the Bedford Airport to get 2 
planes and 1 shipboard set into good operating 
condition. Although briefiy plagued by aircraft 
engine trouble, the demonstration was success- 
ful ; indeed, many laboratory members felt that 
it was too successful, since temporarily there- 
after the urgent requests of the leaders of other 
projects for more personnel were not met. 

Flight Testing 

Bedford Trials 

Starting with the first AEW-equipped plane 
whose radar operated reasonably well on its first 
flight in August 1944, continuous flight testing 
of AEW was carried on from the Bedford Air- 
port until the end of World War II. Three experi- 
mental planes were eventually fitted out at Bed- 
ford. A fourth set was kept operating on the 
bench to try out new ideas on the ground, and 
also to serve as a spare, the components of which 
could be substituted at short notice for defective 
components in the planes. The first two experi- 
mental shipboard systems were also set up at 
Bedford and operated from there for many 
months. The third shipboard set, scheduled for 
Navy trials at Brigantine, New Jersey, was put 
into operation during December 1944 in MIT 
Building 20 in order to simulate more closely 
the heavy interference conditions expected in 
actual operation. 

Results of Tests 

To the dismay of the research workers, the 
complex system jammed itself; that is, inter- 
ference was so bad that rotational data, trans- 
mitted by a double-pulsed code over the relay 
link, was almost completely jammed. Under the 
threat of possible failure for the program, how- 
ever, a triple-pulsed coding system was devised 
and incorporated by around-the-clock work into 
all experimental synchronizers, relay receivers. 


and decoders. With many misgivings on the part 
of the engineers because of inadequate testing of 
this change, the third shipboard experimental 
set (SX-3) and the second airplane with AX-3 
were shipped to Brigantine for the U. S. Navy 
trials about the first of January 1945, only two 
weeks behind schedule. Fortunately, the new 
coding system performed well. 

During the hectic month of December 1944, 
the project engineer, W. P. Dyke, contracted an 
illness which made him unavailable for the dura- 
tion of the AEW program. Unfortunately just at 
this time the U. S. Navy’s pressure for early pro- 
duction deliveries increased. At a meeting in 
early December called by the Deputy Chief of 
Naval Operation (Air) , the fleet’s great need for 
AEW to combat low-flying planes and the Kami- 
kaze attacks was officially disclosed. An over- 
riding priority was added to the already top 
position of AEW in the electronics field. The 
Navy made available to the laboratory crews of 
officers, technicians, and draftsmen as fast as 
they could be assimilated. A special air transport 
service to facilitate deliveries of parts and per- 
sonnel transportation was also set up by the 
Navy. 

Production 

Organization 

In July 1944, before the first of the experi- 
mental models of AEW had even been flown, the 
importance of solving the early-warning prob^ 
lem had increased to such an extent that the 
Navy officially confirmed its earlier indication 
through NDRC that the MIT-RL and RCC under- 
take production of forty complete systems. Pro- 
duction planning and a number of large produc- 
tion subcontracts were immediately started, 
thus making the program truly “crash,” with 
research, development, and production proceed- 
ing concurrently. 

In order to achieve the coordination necessary 
for engineering, production, and delivery by 
RCC and the 30-odd major and multitudinous 
minor subcontractors of the laboratory, respon- 
sibility for this phase of the activity was largely 
delegated to R. J. Woodrow. C. M. Kelly, previ- 
ously in charge of radar research and develop- 
ment, was designated the production engineer 
for the airborne section. A. C. Byers, in addition 


AEW CADILLAC I SYSTEM 


93 


to his duties as project engineer on other ship- 
board research and development, was chosen as 
the project engineer for the shipboard section of 
AEW. Weekly meetings were initiated with RCC 
in November 1944; close liaison was maintained 
with the laboratory subcontractors and many of 
their engineers spent a substantial portion of 
their time in Cambridge. 

Production Scheduling 

It might appear impossible to schedule re- 
search and development in any detail ; if the com- 
ponent parts and steps to be taken were known 
in advance, no research and development would 
be necessary. However a rather unorthodox, and 
to a certain extent backward, process of schedul- 
ing was attempted on the five AEW experi- 
mental systems. The estimates, based on previ- 
ous experience of the Division 14 heads and 
group leaders concerned, were combined to give 
target dates for the delivery of each system. Then 
as designs crystallized and construction began, 
more detailed target dates for components and 
subcomponents were projected backwards from 
the system target dates. 

Bottlenecks were thus discovered, and addi- 
tional effort was concentrated on them by in- 
creasing personnel or expediting critical pro- 
curement items, by special attention in the shop, 
or by any other shortcuts that could be devised. 
Although the original target dates were missed 
by times ranging from two weeks for the first 
system to two months for the fifth (which had 
many features not originally contemplated) , the 
results were far better than most people had ex- 
pected. The scheduling procedure used is be- 
lieved to be the only type generally practicable 
for research and development ; even with it, re- 
sults would have been poor had the project not 
had a high priority. 

Design Changes 

Since research and development were proceed- 
ing in parallel with production, a very flexible 
method for incorporating changes was essential. 
A number of target dates for final freezing of 
design were set, each one advanced over the pre- 
vious date ; but actually there never was a final 
“freeze’" date, but instead, a progressive elimi- 
nation of the number of modifications to be made 
in designs which were in various stages of 
production. 


Delivery Scheduling 

The original production schedule proposed to 
the Bureau of Aeronautics in June 1944 prior to 
the formal request for production, was to start 
deliveries with two complete systems in Febru- 
ary 1945. In November 1944 a revised schedule 
was presented which called for the delivery of 
1 system in March 1945, followed by 4 in April 
and approximately 8 per month thereafter. Al- 
though very great efforts were later made to 
advance this schedule, the final deliveries, except 
for items subsequently added to the system, for 
the most part conformed to this delivery date. 

Type Testing 

The fourth of the five experimental airborne 
and shipboard sections of AEW built at the lab- 
oratory were scheduled to go to RCC as proto- 
type units and to serve as the first complete test 
bench system into which early production com- 
ponents could be substituted and tested. It had 
been hoped that, prior to delivery to RCC, these 
units could be type tested for altitude, tempera- 
ture, humidity, and vibration. However, the pres- 
sure of time and the delays in delivery of ade- 
quate test apparatus made it impossible to test 
more than a few of the critical components. To 
supplement these tests, complete type tests were 
run on one of two extra systems constructed. Sev- 
eral necessary modifications were revealed by 
these tests and modification kits were prepared 
and distributed. 

Performance Testing 

Performance testing of each production com- 
ponent as it came off the production line was 
handled by complete and in some cases elaborate 
test procedures. Following the individual com- 
ponent tests, all the critical components of the 
system were assembled at RCC and tested in 
complete bench systems, of which two and the 
elements of a third were eventually established. 
This was a quite radical departure from previous 
radar production practices, but proved necessary 
because the space, facilities, and personnel avail- 
able were inadequate for the assembly and test 
of all the components of each of the 40 systems 
at the same time. Such a procedure also made it 
possible to test and deliver in advance those air- 
borne components requiring the longest time for 
installation in the planes. 


94 


PROJECT CADILLAC, AEW RADAR SYSTEMS 


Maintenance Program 

In view of the complexity of the Cadillac sys- 
tem (the airborne and shipboard sections each 
contained approximately two hundred vacuum 
tubes not counting those in the standardized 
units) a comprehensive maintenance program 
was planned, and at the Navy’s request, the lab- 
oratory presented in July 1944 complete recom- 
mendations for maintenance after installation. 
These recommendations included the spare parts 
to be furnished, a tentative list of the test equip- 
ment believed necessary, the complement of 
maintenance and operational personnel which 
should be trained, and the importance of having 
a complete bench test system of the airborne sec- 
tion, and a stand-by shipboard section aboard 
each carrier equipped. 

Spare Parts. Between the time that these rec- 
ommendations were prepared and the time of 
final installation and use, a year of many develop- 
ments intervened. To provide greater flexibility, 
each equipment was provided with enough spare 
parts to insure approximately one year’s opera- 
tion. Seventy per cent of the test equipment orig- 
inally proposed was either modified or replaced 
by other items. 

Instruction Manuals. It was obvious from the 
start of the AEW project that such complex 
equipment would require comprehensive instruc- 
tions for maintenance and operation. MIT-RL’s 
publications group (Group 35.2) and a subcon- 
tractor, the Jordanoff Aviation Company, pre- 
pared the text and illustrations for the 820-page 
airborne and 570-page shipboard maintenance 
manuals. Some writing and a substantial editing 
job remained, which were handled by the staffs 
of the airborne and shipboard production engi- 
neers and by Lieut. Robert Kellner of the Navy. 
Preliminary handbooks to cover the mainte- 
nance of the experimental models during Navy 
trials served as prototypes for the final manuals. 
Owing to the large number of modifications ulti- 
mately made in the production systems, final 
shipboard instruction manuals were not avail- 
able for most of the training stages and the first 
several installations, so that a sufficient quantity 
of interim handbooks were hectographed for 
these purposes. Handbooks of instruction had 
also to be prepared and published for 12 of the 18 
test instruments supplied by MIT-RL and RCC. 


^•2-^ U. S. Navy Trials 

Center of Operation 

Navy trials of the experimental AEW systems 
had been contemplated early in the program; 
these eventually included not only operations at 
the CIC Group Training Center, Brigantine, 
New Jersey, but also installation and operation 
of the equipment on board the carrier USS 
Ranger. 

Reorganization of Project 

The third airborne and shipboard experi- 
mental sections of AEW, following the flight 
tests at Cambridge previously described, were 
put into operation at Brigantine during the first 
part of January 1945. Many problems, some 
foreseen and others not, were almost immediate- 
ly encountered. To accelerate their solution, a 
substantial reorganization of the project at the 
laboratory was made about the first of February 
1945. The new organization operated essentially 
as a separate laboratory division known as 
Project Cadillac. J. B. Wiesner, project engi- 
neer, was in charge. He was assisted by R. Rollef- 
son, project engineer for the airborne section, 
and R. E. Meagher, project engineer for the ship- 
board section. R. J. Woodrow continued as asso- 
ciate project engineer for production. 

Project Cadillac coordinators were appointed 
in the office of CNO and in BuAer and BuShips. 
BuAer in particular assigned a substantial staff 
to the project. 

Incorporation of Modifications 

Even before the Brigantine tests were com- 
pleted, most of the improvements recommended 
were well underway and being tested at Bedford. 
Modifications were incorporated in the ship- 
board relay receiver and decoder to improve 
their performance under conditions of inter- 
ference. NRL, which had previously collabo- 
rated in the solution of mutual interference 
problems in the airplane, worked out the design 
of filters for other types of shipboard electronic 
equipment to prevent their transmitting appre- 
ciable amounts of energy at the relay frequency. 
Special anticlutter circuits were developed for 
the radar receiver to facilitate the distinguish- 
ing of signals through the clutter of echoes at 
close ranges from the surface of the sea. 


AEW CADILLAC II SYSTEM 


95 


Sea Trials 

While the Brigantine trials were still under- 
way, the equipment for sea trials aboard the 
USS Ranger was made ready and shipped to the 
West Coast. When the planes joined the carrier 
in April 1945, the installation was essentially 
complete and tests started almost immediately. 
The Ranger trials lasted for two months, and 
appeared to establish the value of AEW beyond 
question. Following close upon the end of the 
war, at least two carriers, the Enterprise and the 
Bunker Hill, made trial cruises during which 
AEW was used. 

Performance Data 

During the trials of the AEW Cadillac I sys- 
tem, much data on performance were collected. 
It was found that single aircraft of torpedo 
bomber size, flying at 500 ft, can be consistently 
detected at ranges of 45 to 70 miles with the 
AEW plane flying at 2,000- to 5,000-ft altitudes. 
This is twice the range of the best shipboard 
radar system on similar targets. Groups of 6 to 
14 planes at 500 ft were detected at ranges vary- 
ing from 60 to 120 miles, or two to four times 
the range of shipboard sets. Surface vessels of 
destroyer size or larger can be detected at 200 
miles with the AEW plane flying at 20,000 ft, 
increasing by a factor of six the previously avail- 
able range. The relay equipment proved reliable 
out to 45 miles from the receiving ship, thus 
making possible a further extension of the detec- 
tion range in the direction of the AEW plane. 

8.3 AEW CADILLAC II SYSTEM 
Initiation of Program 

In June 1945, while the Cadillac I program 
was at its peak, reports from the fleet indicated 
the need for the type of long-range reconnais- 
sance, warning, and control made available by 
AEW, but in locations unsuitable to the opera- 
tion of ships having AEW shipboard equipment. 
Upon request from the Navy to NDRC, MIT-RL 
initiated the Cadillac II program. This program 
contemplated the development and production of 
the necessary equipment for an airborne combat 
information center [CIC] in a four-engine 
bomber. Such a system had been considered 
much earlier, but MIT-RL and Project Cadillac 


were already so heavily engaged that it required 
an expression of the top priority of the program 
before it could be undertaken. 

Design of Cadillac II 

As conceived almost from the start, Cadillac II 
embraced the installation of all the previously 
developed Cadillac I airborne equipment plus a 
much increased complement of Navy-furnished 
communications gear. The new element in the 
system consisted of the CIC equipment, which 
was installed in the completely remodeled bomb 
bay of the plane. Large 12-in. off-center PPFs, 
equipment for ground-stabilizing the PPI pre- 
sentation, and various associated apparatus 
were the major new contributions of MIT-RL. 
Plotting boards and most of the nonelectronic 
accessories for the CIC were developed and pro- 
duced by the special devices division of BuAer. 
Modifications of the planes and installation of 
the equipment were again handled by NAMU. 

8.3.3 Development and Production 

When Cadillac II was initiated, the construc- 
tion of 11 complete systems was contemplated, 
for which 11 sets of the Cadillac I equipment 
were to be diverted. The quantity was progres- 
sively increased to 13, then 17, and finally 25 ; 
this was eventually cut back to 17 at the end of 
the war. 

Many of the same problems of development, 
testing, and production that were encountered 
in Cadillac I also appeared in Cadillac II, but to 
meet the very tight schedule (and since the scope 
of the second program was by dollar cost only a 
fifth of the former) substantially all the produc- 
tion was done at MIT-RL using MIT-RL and 
U. S. Navy personnel. Deliveries of the 17 sys- 
tems started in August and were complete by the 
end of October 1945. 

In addition to the development and production 
of the 17 CIC indicator systems (AN/APA-53) 
plus spares and instruction manuals, Cadillac II 
also included the establishment at the laboratory 
of a complete trainer for the system installed in 
a B-17 fuselage. Simulated data of the radar and 
IFF performance was fed into the radar indi- 
cators by a basic trainer developed earlier as a 
result of a Navy request to NDRC. Shortly after 
the end of the war the first completely equipped 
plane was ready to fly. 


96 


PROJECT CADILLAC, AEW RADAR SYSTEMS 


8.3.4 Applications of Cadillac II 

The Cadillac II program opened up a new field 
for operational and tactical use. The obvious pos- 
sibilities of control of a fleet of aircraft from one 
or more airborne control centers could have 
revolutionized large air operations, and, as ram- 
ifications of the original program, several other 
developments resulted which could have further 
extended these possibilities. An airborne mov- 
ing-target indication [AMTI] system had been 
flown and showed much promise of discriminat- 


ing between moving targets and echoes from the 
ground or sea so that AEW operation over land 
had important possibilities. Designs had been 
completed and contracts let for complete air- 
borne CIC facilities for simultaneous and inde- 
pendent control of several combat air patrols. 
Means for determining the altitude of aircraft 
targets were likewise under study. However, the 
possibilities of Cadillac II, like those of Cadillac I 
(and like all the most advanced wartime develop- 
ments, for that matter) fortunately had no op- 
portunity to be realized in World War II. 


PART III 

HARP-MATERIAL WITH ARTIFICIALLY CONSTRUCTED 
DIELECTRIC CONSTANT AND PERMEABILITY 



I 


Chapter 9 


DEVELOPMENT AND PRODUCTION PROCESSES 


91 INTRODUCTION 

Historical Survey 

T he work reported in this part grew out of 
ideas which had been submitted to NDRC and 
the Radiation Laboratory at the Massachusetts 
Institute of Technology [MIT-RL] in the sum- 
mer of 1941 by one of the authors.^ Work was 
started at MIT-RL in December 1941 and was 
continued there under various organizational 
forms until the end of 1945 when it was trans- 
ferred to the Naval Research Laboratory [NRL] 
under the direction of one of the authors.^ 

The practical aim was the production of tech- 
nically useful thin layers which would reflect 
ultra high-frequency radio waves poorly. The 
work naturally divided itself into two parts : the 
discovery and study of physical principles which 
would lead to the satisfactory construction of 
such layers ; and the various uses to which they 
might be put when obtained. 

The physical principles were contained in a 
memorandum presented to MIT-RL suggesting 
the use of a medium of high dielectric constant 
and/or magnetic permeability, these properties 
being due to conducting (ferromagnetic) flakes 
suspended in a neutral organic binder. It will be 
shown below in detail why such a medium could 
be expected to have high electric and magnetic 
polarizability and how the possession of such a 
substance enables one to construct technically 
useful absorbing layers.^-^ 

It was obvious at the start of the work that 
such materials once obtained would have many 
useful applications. Protection against radio 
waves was desirable in many instruments and 
arrangements connected with friendly transmit- 
ters. It was similarly desirable as camouflage 
against enemy transmitters. Selectively absorb- 
ing layers could be used similarly for identifi- 
cation purposes; a simple reasoning given in 
Section 11.2.1 shows that every selectively ab- 
sorbing layer can easily be transformed into a 

aO. Halpern. 
bM. H. Johnson 


selectively transmitting layer, i.e., a selective 
filter. Chapter 12 of this report is devoted to 
a detailed discussion of various forms in which 
such applications can be made practical. 

9.1.2 Physical Concepts Underlying HARP 

The idea of using suspended magnetic par- 
ticles to obtain an artificially ferromagnetic 
body of high magnetic susceptibility has been 
attempted many times. The different and more 
favorable results obtained by the present method 
are due to a special feature which can be ex- 
plained on the basis of simple electrostatic and 
magnetostatic analogies. 

The a-c magnetic permeability of a powder 
is not only limited by hysteresis, eddy-current 
losses, magnetic relaxation, etc., but also mostly 
by the demagnetizing effect of the individual 
particles. This difficulty, for example, has been 
a dominant factor in the well-known work of the 
Bell Telephone Laboratories [BTL] staff ; these 
engineers compressed and deformed the orig- 
inally spheroidal particles to obtain shapes of 
smaller demagnetizing factors. As far as known, 
there have been no previous attempts to produce 
an artificial dielectric constant of large value by 
the aid of suspended particles. Since the discus- 
sion for the electric and the magnetic case is 
perfectly symmetrical, the treatment of the 
dielectric constant will be given first. 

The depolarizing factor which is identical 
with the demagnetizing factor depends on the 
shape of the particle exclusively. Although the 
mathematical treatment is restricted to ellip- 
soids, shapes of practical interest can be ap- 
proached as limiting cases. 

It is well known that a plate-like ellipsoid 
shows the largest depolarizing factor if the elec- 
tric vector is directed perpendicularly to the 
surface of the plate ; the depolarizing factor be- 
comes small if the electric vector lies in the plane 
of the plate. The very simple expedient suggested 
for the construction of media of high dielectric 
constant consisted in the use of flakes the short 


CbecrEt ,7 


99 


100 


DEVELOPMENT AND PRODUCTION PROCESSES 


dimension of which was very small compared to 
the long dimensions, and which were preferably 
oriented with one of their long dimensions 
parallel to the electric vector. Threads lying 
parallel to the electric vector would be similarly 
useful but suffer from the disadvantage that 
they cannot be produced as easily as flakes. 

The result of the first experiment made with 
such flakes at MIT-RL showed the feasibility of 
these ideas. Commercial aluminum flake mixed 
with an organic liquid was spread on paper by a 
brush and allowed to dry. The thin layer of alum- 
inum flake thus produced had a dielectric con- 
stant of about 500 in the wavelength region of 
10 cm. 

The problem of calculating the electric or mag- 
netic susceptibilities of a medium thus composed 
is extremely difficult, if not almost impossible, 
at the present state of theoretical physics. The 
only available basis for an estimate is offered by 
the Lorenz-Lorentz formula which is known to 
be quite incorrect and to underrate the values 
obtained. This is particularly true here since the 
size of the constitutive particles is by no means 
small compared with their average separation 
so that the mutual interaction cannot even ap- 
proximately be described as a dipole effect. The 
huge divergencies between the numbers given by 
Lorenz-Lorentz formula and the actual measure- 
ments may be illustrated by one sample which 
gave for the dielectric constant 165 and 2,700, 
respectively. 

9 2 theory and characteristics 

OF HARP 
Introduction 

From the discussion of Sections 9.1.1 and 

9.1.2, it is clear that there are three essential 
elements in the fabrication of HARP, namely, 
the composition and geometrical properties of 
the conducting flakes which are used as pigment, 
the binder in which the flake is suspended, and 
the process for combining the flake and binder. 
These elements are the subject of Sections 9.2.2, 

9.2.3, and 9.2.4. The concluding section deals in 
greater detail with the spraying process which 
has been developed to the point of production in 
a pilot plant.^-29 


The electromagnetic behavior of HARP is 
characterized completely by its dielectric con- 
stant € and its permeability /x. These quanti- 
ties depend on all the parameters of the three 
elements mentioned above. Although the quali- 
tative discussion of Sections 9.1.1 and 9.1.2 per- 
mits an estimate of the way e and jj, depend 
on these parameters, the estimates are neces- 
sarily rough. The mathematical difficulties of a 
quantitative theory have been mentioned. Con- 
sequently, the quantitative relationship between 
€ and juL and these parameters have been de- 
rived from experiment. The information is, how- 
ever, rather incomplete partly because experi- 
ments were only conducted to determine data 
essential to problems at hand and partly be- 
cause many of the factors in the fabricating 
processes were not brought under precise con- 
trol. 

Conducting Flakes 

The materials from which conducting flakes 
are obtained have been either metals or some 
form of carbon. The intrinsic electrical proper- 
ties of these materials are characterized by their 
conductivity and magnetic permeability. Ferro- 
magnetic metals are used to impart permeability 
to the completed HARP film. The additional fac- 
tors involved in their use will be discussed in the 
last paragraph of this section. 

The factors, other than the intrinsic electrical 
properties of the conductor, which govern the 
dielectric constant and permeability of HARP, 
are the size and shape of the conducting parti- 
cles. The size must be sufficiently small that the 
electromagnetic field extends throughout the in- 
terior of the particle and the shape must have a 
small depolarizing factor for the direction of the 
applied electric field. The small dimension of the 
metallic particles must be of the order of 1 
micron or less for microwave applications 
whereas graphite or carbon particles may be 
much larger (in the ratio of the square root of 
the resistivities) . These thickness values are set 
by the skin depth of the conductor in question. 
The shape of metallic particles has always been 
disklike rather than threadlike because the latter 
form is much more difficult to produce. Either 
form has a small depolarizing factor for an elec- 
tric field parallel to the long dimension. Metallic 


THEORY AND CHARACTERISTICS OF HARP 


101 


particles with an average diameter to thickness 
ratio from 15 to 70 have been used. The efficiency 
of the particles in imparting a dielectric con- 
stant to the HARP film increases very rapidly 
for increasing values of the diameter-to-thick- 
ness ratio. 

Graphite in some forms has a natural disklike 
structure. Metallic particles on the other hand 
must be treated to produce the requisite shape. 
Either a hammer or a ball mill are used for this 
purpose. The ball mill is preferable because the 
resulting flake is much more uniform in size and 
shape. Nevertheless flake from a ball mill con- 
tains particles whose parameters vary by more 
than a factor 2. This distribution in size and 
shape is one of the reasons that an exact corre- 
lation has not been established between the par- 
ticle parameters and the HARP properties.® 

The conductivity determines the skin depth of 
a conductor at a given frequency ; consequently, 
as the frequency is increased, the dielectric con- 
stant of HARP begins to decrease when the skin 
depth becomes of the order of the particle thick- 
ness. Thus, for microwave HARP, the real part 
of the dielectric constant is independent of the 
frequency for all lower frequencies. At a suffi- 
ciently high frequency the dielectric constant 
begins to decrease. The conductivity also influ- 
ences the imaginary component of the dielectric 
constant for it determines the energy dissipa- 
tion of currents which flow when the particles 
are polarized by the applied field. The losses are 
greater for conductors with low conductivity. 
Hence, the incorporation of carbon or graphite 
in HARP film increases the imaginary compo- 
nent of the dialectric constant. 

The preparation of ferromagnetic flakes in 
general has a detrimental effect on the magnetic 
properties of the metal. Those metals and alloys 
with very high permeability are particularly 
sensitive to mechanical and heat treatment and 
therefore are most affected by the milling proc- 
ess. Efforts to restore the magnetic properties 
by annealing the flake have met with indifferent 
success because annealing at the required tem- 
peratures deforms the particles. Nevertheless, 

t^Metallic flake has been obtained from many companies 
engaged in manufacturing metal powders. However, 
most of the experimental work on flake used for the 
HARP program was done at the Metals Disintegrating 
Company, Elizabeth, N. J. 


a number of HARP films fabricated from ferro- 
magnetic metals suitable for resonant absorbers 
have shown permeabilities of about 2 at 10 cm 
and about 7 at 150 cm. Films have also been pro- 
duced with permeabilities in the neighborhood 
of 20 at 150 cm. However, they had too great an 
absorption coefficient to be effective as resonant 
absorbers. 

Binders 

The binder of a HARP film is primarily a me- 
dium for supporting the metal flake. It is mainly 
responsible for the mechanical properties of the 
material. Its electrical characteristics also have 
some influence on the dielectric constant of 
HARP. 

The binder must be of such a nature that the 
metallic flake can be used as a pigment. Hence, 
either organic compounds which may be dis- 
solved or suspended in a liquid, or semi-liquid 
rubber compounds which set after moderate heat 
treatments have been used. Ceramic materials in 
which it is also possible to mix the metal parti- 
cles before firing have not been tried because the 
flexibility of the HARP film is an important ad- 
vantage in most applications. The choice of 
binder in the wide field indicated is dictated by a 
combination of mechanical and electrical con- 
siderations, as well as by the actual fabrication 
method. 

Tough, flexible films containing a high per- 
centage of metal can be produced from a number 
of organic polymers. The most successful of 
these have been artificial rubbers such as GR-S 
and neoprene. Films of excellent mechanical 
qualities have been made with neoprene and car- 
bon black in the ratio 2 to 1 with metal concen- 
trations (aluminum) in the neighborhood of 
25%. Films of good mechanical quality have 
been formulated from GR-S with metal (alumi- 
num ) concentrations as high as 75 % . These films 
withstood prolonged out-of-door exposures and 
were undamaged in severe accelerated rain tests 
on the camber surface of aircraft propellers. A 
thin nylon topcoat provides resistance to oil and 
similar liquids. 

The bonding of the film to metal backing foil, 
usually 2-mil Al, has been most successfully ac- 
complished by a Goodyear rubber cement with 
the trade name of Pliobond. The cement is 


102 


DEVELOPMENT AND PRODUCTION PROCESSES 


sprayed on the foil and the film sprayed directly 
over it in this fabricating process. In other cases 
the cement is sprayed on the foil and the bond is 
set in a hot press. These bonds are almost as 
strong as the material itself. The metal backing 
is bonded to the surface to be covered by a pres- 
sure sensitive adhesive, L-115, manufactured by 
the B B Chemical Company. Bonds of adequate 
strength have thereby been obtained even when 
the covered surface is itself metal. 

The principal effect of the binder on the elec- 
trical properties of HARP arises from dielectric 
loss in the binder. This contributes to the imagi- 
nary component of e and is important in films 
whose absorption index must be kept low. In 
other cases the loss in the binder is used to effect 
the proper absorption index for a resonant ab- 
sorber. Of the two binders mentioned above, 
GR-S has a very low loss so that the absorption 
in HARP fabricated from it is mainly due to the 
metal flakes. Neoprene, on the other hand, has a 
considerable dielectric loss which is enhanced by 
the addition of carbon. Absorption in HARP 
fabricated from it is almost entirely due to the 
binder. 

9.2.4 * Fabricating Processes 

A number of fabricating processes for com- 
bining the flake and binder to produce a result- 
ing film are available. They differ mainly in the 
degree of alignment of the metal flakes parallel 
to the surface of the film that can be achieved. 
They fall into two classes. In the first the mixture 
of flake and binder is effected in a liquid solu- 
tion or suspension of the binder. The film is con- 
structed of successive layers laid down by a knif- 
ing or spraying technique, the solvent being 
evaporated by drying each layer. When the film 
has been built to the proper thickness, it is cured 
at a temperature usually about 130 C to obtain a 
stable product. In the second class the metal is 
mixed with the flake in a rubber mill. The prod- 
uct is then calendered into thin sheets. The final 
product is obtained either by laminating the 
sheets to the desired thickness in a hot press or 
by forming a large block in the same manner 
from which the desired sheets are sliced. 

The behavior of HARP with varying concen- 
trations of metal is similar for all the fabricat- 
ing processes. A typical example is shown in Fig- 



Figure 1. Variation of refractive index with metal 
concentration. 


ure 1. The index of refraction (= \/«) bas been 
plotted as the metal concentration, given as per- 
centage by weight, is changed. In the lower part 
of the curve, clay has been added to the binder to 
keep the film from being excessively soft. Identi- 
cal flake was used for all samples. It will be noted 
that the curve is at first approximately linear 
and rises very rapidly at the higher metal con- 
centrations. The absorption index for refractive 
indices between 25 and 45 is approximately cor- 
rect for resonant absorbers. For higher refrac- 
tive indices it is too great while for lower refrac- 
tive indices it is too small. Hence, for each binder 
and flake there is a region of refractive indices 
which are associated with the correct absorption 
index to give HARP suitable for a resonant ab- 
sorber. 

In processes of the first kind, a high degree 
of flake alignment is attained by depositing 
the film in successive layers. As the solvent evap- 
orates, the surface tension aligns the particles 
parallel to the film. In addition to the theoretical 
considerations of Sections 9.1.1 and 9.1.2, very 
early experiments at MIT-RL showed the im- 
portance of this factor in imparting a high di- 
electric constant to HARP. For example, a flake 
and binder which yields e = 2,500 when fabri- 
cated by spraying may give a dielectric constant 
less than 100 when no effort is made to align the 
flake. 

Of these processes, the knifing technique was 
first used to obtain considerable quantities of 
film. Each layer was deposited by a knife the 
height of which above a very flat piece of glass 


THEORY AND CHARACTERISTICS OF HARP 


103 


was carefully controlled. By knifing successive 
coats at right angles a nondirectional film of 
high index was obtained. Although a substantial 
amount of film was produced in this way, no 
other method being available at the time, it is 
highly unsatisfactory as a production process, 
both from the standpoint of uniformity in the 
product and of cost. Much better films were ob- 
tained by knife-casting on a large wheel. How- 
ever these films were necessarily directional in 
their properties, having a 30 per cent higher 
dielectric constant in the direction of the knife 
stroke. 

A number of attempts were also made to 
knife-cast film on long sheets of cloth carried 
over rollers. This method also gave nonuniform 
materials which were highly directional. The 
method finally evolved to produce nondirectional 
film of uniform quality was that of spraying suc- 
cessive layers on a foil base. It will be more fully 
discussed in Section 9.2.5. In this process a sys- 
tem of electrical testing could be incorporated to 
control the production at various stages so that 
it was not necessary to keep the numerous vari- 
ables of the process absolutely constant. 

The second class of processes yields a much 
lower degree of flake alignment and is therefore 
useful for HARP of low refractive index. As 
the thicknesses are then much greater, all toler- 
ances are correspondingly increased. If, in addi- 
tion, the variable factors arising from solvents 
are removed by avoiding the use of solvents, the 
whole process can be sufficiently well controlled 
so that tests on a single sample of a batch suffice 
to determine the required thickness for the whole 
batch. This is essential for production by these 
processes as there is no simple method of adjust- 
ing the thickness after the film is formed. 

The binder and pigment are generally mixed 
in a rubber mill and then calendered into sheets 
between 10 and 50 mils in thickness. Each sheet 
is quite directional with a higher dielectric con- 
stant along the length of the sheet. In the press- 
curing method these sheets are cross-laminated 
and press-cured to the proper thickness. In the 
slicing process the sheets are cross-laminated, or 
otherwise formed to reduce directionality and 
are press-cured in a large chase. The material is 
sliced from the block by a machine knife. Films 
of very uniform thickness have been made in 


this fashion. Plant trials in which 25 to 50 sq yd 
of HARP were fabricated indicate that this will 
be an entirely satisfactory production method 
for low-index HARP. 

9.2.5 Pilot Plant Production 

After the spraying method had proved suc- 
cessful on a small scale, a pilot plant for the pro- 
duction of HARP was assembled by the Du Pont 
Company at Newburgh, N. Y. It contained four 
essential elements : the spray machine and asso- 
ciated ventilating equipment, a belt dryer, cur- 
ing ovens, and electrical test equipment. The 
cement composed of binder, solvent, and flake 
was prepared at another plant of the company. 

A transverse DeVilbiss spraying machine was 
found to be very satisfactory. The gun traveled 
transversely over the panels to be sprayed at an 
adjustable height. When a proper spray pattern 
had been determined by varying the height and 
speed of the gun, the pressure at the gun, the 
speed at which the panels were carried under the 
gun, the viscosity of the spray fluid, etc., 20-mil 
films could be sprayed in about 30 coats the total 
thickness of which varied by less than a mil over 
the surface of the film. 

The aluminum foil on which the film was 
sprayed was affixed to a sheetrock base to insure 
that the foil was perfectly flat. At the end of the 
process, the completed films were stripped from 
the base. The panels, 4 ft by 2 ft, were normally 
carried through the spraying cycles in pairs. 
After passing under the gun, the belt conveyor 
carried them through a dryer to remove the sol- 
vent before the next application. At the end of 
each cycle the panel was rotated through 90° 
to remove all trace of directionality in the final 
product. In the last few cycles, electrical tests 
for the resonant absorption were made to deter- 
mine the point at which the process should stop 
to produce the requisite film. The testing was 
essential as the resonant wavelength, and con- 
sequently the thickness, had to be held to 1 per 
cent. After a panel had been sprayed to the 
proper thickness, it was subjected to a tempera- 
ture cycle in the curing ovens. The curing tem- 
peratures required careful adjustment to yield 
a stable product. Small changes in the resonant 
wavelength of a film as a result of curing were 
known in advance so that the uncured panels 


104 


DEVELOPMENT AND PRODUCTION PROCESSES 


were adjusted to a thickness which would yield 
the required resonant wavelength after curing. 

The capacity of this plant was limited by the 
drying cycle and the handling of the panels. It 
was operated on a 24-hour basis and could pro- 
duce somewhat more than 1,000 sq yd a month. 
The plant was first used to produce some 1,500 
sq yd of S-band film.^^ It was later operated under 
a Navy contract to produce about 2,500 sq yd of 
X-band HARP and 600 sq yd of S-band HARP. 

The Navy specifications, NAVAER-M-710/ 

Under OSRD Contract OEMsr-1199. 


M-712, required that X-band HARP, designated 
as MX-410/AP, should have a power reflection 
coefficient less than 4 per cent over the wave- 
length band from 3.18 cm to 3.22 cm when tested 
at a 30° angle of incidence. The film was approxi- 
mately 20 mils thick. The specification NAVAER 
M-710/M-711 for S-band HARP, designated as 
MX-355/AP, required that the power reflection 
coefficient be less than 5 per cent over the wave- 
length band from 9.04 cm to 9.16 cm when tested 
at a 30° angle of incidence. The film was about 
50 mils thick. 


Chapter 10 


ELECTROMAGNETIC PROPERTIES OF HARP 


1 PROPAGATION IN A DIELECTRIC AND 
PERMEABLE MEDIUM 

T he propagation of waves through a medium 
with a dielectric constant e and magnetic 
permeability /a is governed by Maxwell's equa- 
tions. As all the phenomena discussed in this 
report are stationary in type, the field quanti- 
ties vary with time as where (o — 27rv, V being 
the frequency of the field. Thus the electric field 
is the electric induction is the mag- 
netic field is the magnetic induction is 

and the current density is Under 

these conditions Maxwell’s equations are: 


div D = 0, 

(1) 

div B = 0, 

(2) 

curl E = — ikoB , 

(3) 

curl H = — u -f- ikoD . 

(4) 


where 


^ CO 27r 

” C Xo * 


To these equations must be added the constitu- 
tive relations 

u = o-E, (5) 

D = 6oE, (6) 

B = mH, (7) 

where o- is the conductivity of the medium. It is 
convenient to eliminate equation (5) immedi- 
ately by writing the fourth Maxwell equation 
(4) as 

curl H = z/boD, (8) 

and 

D='€E, (9) 

where^ 

2i(j 


€ = eo - 


( 10 ) 


The medium will be assumed uniform. In- 
homogeneous media can be treated as several 
uniform regions separated by boundaries at 
which e and /a discontinuously change in value. 

The dielectric constant and magnetic permea- 
bility are in general complex. Thus 

€ = €r — ^€^, (11) 

At = Mr — ^Mi• (12) 

€i and Mi niust be positive if the corresponding 
terms in the equation for the Poynting vector 
represent energy dissipation. The imaginary 
part of e may arise from conduction currents 
through the medium and from dielectric loss. 
The imaginary part of m is introduced to ac- 
count for a high-frequency magnetic loss, 
distinct from hysteresis and eddy-current 
losses, which is known to exist. It is tentatively 
ascribed to a relaxation time for magnetization. 

In an isotropic medium simple elimination 
leads to the following propagation equation 
which is satisfied by all components of E and H. 

VV + 6mA:>=0. (13) 

Plane waves of the type exp (— • r) are 

solutions of this equation where 

/c = €M . (14) 

If the propagation vector is along the positive 
z axis, the electric and magnetic fields are given 
by 

E= (15) 


H 


= - A 

\ M 


(16) 


Wave propagation given by the solutions of 
these equations is essentially determined by the 
quantities c and m* 

‘In the case of Cu at a frequency of 3xl0®c(\o = 10 
cm), the imaginary part of e is 3.42x10®. 


This is a damped wave whose wavelength is 
determined by the real part of the propagation 
constant and whose damping constant is deter- 
mined by the imaginary part. 

k = kr — iki (17) 

kr = ko ^ \e\ ImI cos i tan~^— -j- I tan“^ — 1 (18) 

L €r MrJ 

// |e| ImI sin I I tan“^ " + i tan“^ —1 • (19) 

L €r Mr j 


ki = ko 


105 


106 


ELECTROMAGNETIC PROPERTIES OF HARP 


It will be noted that positive ei and fn are re- 
quired in order that the wave diminish in 
amplitude for increasing positive values of z. 

It has been previously observed that HARP 
materials contain metal flakes which are aligned 
to a greater or less degree with the surface of 
the material. Consequently the electrical prop- 
erities are anisotropic; e and fx must be con- 
sidered tensor quantities. Because the same me- 
tallic flakes give HARP its dielectric as well 
as its magnetic properties, the principal axes of 
the e and fi tensors necessarily coincide. Fur- 
thermore, in most cases, two of the three prin- 
cipal components of c and of /x are equal. Let 
X, y, and z be the principal axes of the e and /x 
tensors and let €i,/xi be components of the ten- 
sors along the x and y axes while e 2 ,iu ,2 are the 
components along the z axis. Equations (6) and 
(7) may be written 

D* = €iF*, 

Dy = eiEy, (20) 

Dg — ezEg. 

Eg — 

By = fiiHy, (21) 

Bg = n2Hg. 

For subsequent use it is only necessary to 
treat the case in which Eg or Hg is zero. In the 
first case the solution to the above equations is 
given by 



E = 

(22) 


k 

Hg= -A — e-*(***+^*^>, 

Mi^o 

(23) 


^2^0 

(24) 

where 

vector 

the components of the propagation 
satisfy the relation 


kl + '^k\^t^mkl. 

Ml 

(25) 

In the 

second case the solution is given by 



Ex — , 

(26) 


Eg — —A — - e-* (***+*•*> , 

e2kg 

(27) 


H = = A 

kg 

(28) 


where the components of the propagation vec- 
tor satisfy the relation 

(29) 

€l 

In the application to be discussed later, k\ is 
small compared with As a result kg is very 
nearly given by and the effects arising 

from anisotropy in e and /x are all of second 
order. 

2 electromagnetic MEASUREMENTS 
ON THIN SAMPLES 

The determination of the dielectric constant 
and magnetic permeability of HARP materials 
can be conveniently effected by mounting thin 
samples in a waveguide or coaxial line. A 
slotted section is used to measure the phase and 
amplitude of the wave reflected by the sample. 
If the line is shorted by a metallic plug a 
quarter wavelength behind the sample, the sam- 
ple is in a region of strong electric field and 
weak magnetic field. The phase and amplitude 
of the reflected wave then depend only on the 
dielectric properties of the HARP material. If 
the line is shorted directly behind the sample, 
the sample is in a region of strong magnetic 
field and weak electric field. The phase and 
amplitude of the reflected wave then depend 
only on the magnetic properties of the HARP 
material. A detailed discussion of this method 
of determining c and /x follows. 

Consider first the propagation in a coaxial line 
whose inner conductor of radius a and outer of 
radius h are supposed ideal conductors. The 
boundary conditions on these surfaces are that 
the tangential component of E and the normal 
component of H be zero. If the cylindrical co- 
ordinates z, r, and be used, the solution of 
equations (1-7) which correspond to the normal 
type of coaxial transmission are 


r 

(gu. ^ ^ 

(30) 

II 

1 

J- a'e-**") , 

(31) 


where k is given by equation (13). It is conve- 


ELECTROMAGNETIC MEASUREMENTS ON THIN SAMPLES 


107 


nient to introduce the ratio of Er to . Thus 



jjL e*** + q:' e 


€ e 


ikz ^—ikz 


(32) 


The boundary conditions at the surface between 
two sections of the line filled with different 
media (tangential components of E and H con- 
tinuous) can now be replaced by the condition 
that C be continuous across this boundary. 

Let the sample have one boundary at z — 0, 
the other at z = — d. Furthermore let 


Er^- e“'"* 
r 

be the incident wave falling on the sample from 
the left while 


E, = - 
r 

is the wave reflected to the right and a is the 
amplitude reflection coefficient. Then 


f(0) = - (33) 

1 — a 

Hence the amplitude and phase of the reflected 
wave can easily be determined as soon as ^(0) 
is known. 

The two cases of interest are — d) = 0 and 
a-d) = 00 . The first condition corresponds to 
a short circuit directly behind the sample while 
the second corresponds to a short circuit A/4 
behind the sample. In the first case 


so that 


r(o) = 


^-ikd _|_ o^'^ikd = Q ^ 



1 — 

_j_ 0—2ikd 


— ifxkod . 


In the second case 


(34) 


so that 


m 


eikd _ c^'^ikd = Q 



1 -h 

2 ^—2ikd 


-1 

iekod 


(35) 


In both cases use has been made of the fact that 
the sample is thin, (kd) 2 1. If a is determined 
by a measurement of the phase and amplitude 
of the reflected wave, equations (33) , (34) , and 
(35) may be used to find € and fx. It will be noted 
that if €i = /xi = 0, then |a| =1. 


In practice the quantities measured are the 
shift in position I of the minima of the standing 
wave system and the voltage standing wave 
ratio X when the sample is introduced into the 
line. Let 

A = — • (36) 

Xo 

Remembering that the voltage standing wave 

ratio is given by ^ and that phase shift of 
1— |a| 

the reflected wave is given by the argument of 
a, it is found that 

= (37) 


€i = 


1 

kodx * 


(38) 


in case the short circuit is A/4 behind the 
sample. In the magnetic case 



(39) 


1 

xkod 


(40) 


If the phase shift is quite large, the following 
more accurate formulas should be used in the 
dielectric case. 


€r — 1 = — tan A , 

k(}(i 


(41) 


€i = -/l (1 + tan^ A) . (42) 

xkod 

In a rectangular waveguide of width a the 
solution corresponding to the lowest mode of 
propagation is given by 


Ex — A sin — (e**'* a' e -**'*) , (43) 

a 


■ 


sin-(e'‘''-a'e-'*'»), (44) 
a 


where 


H.. = A ^ cos — + a' e -•‘'*) , 

ifiko a 


k'^ = enk 




(45) 

(46) 


108 


ELECTROMAGNETIC PROPERTIES OF HARP 


The expression for C is now 



For the solution in HARP material e and fi 
are always sufficiently large that the term 
(7r/a)“ can be neglected in equations (46) and 
(47) . The equation for C becomes identical with 
equation (32) for the coaxial line. In parts of 
the guide filled by air or material of very low 
dielectric constant, (n/a)^ cannot be neglected 
and gives rise to the well-known difference 
between free-space and guide wavelength. Then 
equation (33) must be replaced by 



Combining equation (48) with equation (34) 
and expressing the results in terms of I and x 
in the same manner as before, it is found that 
for the magnetic case equations (39) and (40) 
still remain valid if the guide wavelength is 
used throughout in place of the free-space wave- 
length. similarly expressions for cr and ci, 
equations (41) and (42) , may be used provided 
that in addition to this change e,. and ci are 
multiplied by the factor [1— (Tr/koa)^]-^. 

Table 1 shows the calculation of dielectric 
constants made from measurements at 10 cm 


in a coaxial line on typical samples. The first 
two samples are of HARP materials while the 
second two are binders consisting of GR-S and 
clay (sample 3) and GR-S and ZnO (sample 4). 

Measurements similar to these have also been 
made in a rectangular waveguide. The wave- 
guide is superior to the coaxial line in that dif- 
ferences in the dielectric constant for different 
orientations of the electric vector in the plane 
of the sample can be measured. The coaxial 
line measurements always yield the dielectric 
constant averaged over all orientations in this 
plane. 

In general, measurements of the dielectric 
constant in thin samples cease to be accurate 
(errors of 10 per cent or greater) when cr 
exceeds 2,000. As a quarter wavelength is then 
about 20 mils, the construction of ledges to sup- 
port the sample in such a way as not to affect 
the measurement is prohibitively difficult. 
Furthermore the presence of air gaps of the 
order of 1 mil between the boundary of the 
sample and the metal walls can cause large 
distortions in the electric field. In these respects 
the waveguide and coaxial methods are ap- 
proximately equally good. The fact that rings 
and ledges can be more accurately turned on a 
lathe for coaxial fittings is roughly compensated 
by the fact that the irregularities in the wave- 
guide are introduced in a region where the 
electric field is not so intense. 


Table 1. Calculation of dielectric constants from 10-cm measurements in a coaxial line. 


Sample 

Thick- 
ness in 
mils 

1 

kod 

Power 
SWR in 
db 

1 

X 

1 in cm 

tan A 

€r 


709-3 

4.0 

156.0 

46.0 

0.0050 

2.414 

18.7 

2,900.0 

270.0 

2076-3 

2.5 

250.0 

29.6 

0.034 

1.092 

0.8 

200.0 

12.0 

2109-1 

84.0 

7.4 

44.0 

0.006 

0.73 

0.48 

3.56 

0.06 

2109-5 

62.0 

10.0 

34.0 

0.020 

0.65 

0.43 

4.3 

0.24 


Chapter 11 


THEORY AND APPLICATIONS OF RESONANT ABSORBENT LAYERS 


1 THEORY OF RESONANT ABSORBING 
LAYERS 


I T HAS already been noted in the introduction 
that the realization of a quarter wavelength 
absorbing layer in a practical form depends on 
the use of material with high refractive index. 
Since this is the most important type of ab- 
sorber, a detailed discussion of its properties is 
given in this chapter. In addition this study 
yields another method for determining e and fi 
which does not suffer from the limitations men- 
tioned at the end of Chapter 10. 

The theory of an absorbing layer which is an 
odd multiple of a quarter wavelength in thick- 
ness is most easily developed for an open space. 
When the general results, including the be- 
havior for waves incident at an oblique angle, 
have been obtained, the necessary modifications 
for an absorber in a closed space (waveguide or 
coaxial line) can be simply made. 

As in Section 10.1, let the boundaries of the 
HARP layer be at 2 : = 0 and z = — d. Atz = — d 
let there be a perfectly reflecting metal plane. 
The solution of Maxwell’s equations for an 
incident wave normal to the layer in the 
medium is 

E= Ey = + a' • (D 

H=//.= -A -o' . (2) 


Introducing C(z) as in equation (32) Chapter 

10 , 




-{• a' e 
— a' 


0>z>-d (3) 


r(2) = 




z>0. 


(4) 


In these equations k is given by equation (14) 
Chapter 10. The boundary conditions are that 
^(—d) = 0 and C is continuous at ; 2 ; = 0. The 
first condition gives 


^-ikd ^ ^+ikd= Q (5) 


The second becomes 


1 + a 
1 — a 


= -m = 



0—2ikd 

1 + e-2i*d 


( 6 ) 


a is again the amplitude reflection coefficient. 

Before examining the resonant case, it may 
be noted that when e= 


a = (7) 

Hence if kid is large, a becomes zero. Therefore 
if a medium for which e = could be con- 
structed with a reasonably large value of €r, it 
could be used for a practical absorbing layer 
which was not resonant. The band width would 
be determined by the extent to which e and fx 
varied with frequency. 

It is clear from equation (6) that, in the 
phase and amplitude of the reflected wave, the 
wavelength and thickness of the layer enter 
explicitly only in the combination k^^d. Over 
the width of a resonant absorption band, e and (x 
change inappreciably. Consequently the res- 
onance curves depend only on Ao and d, through 
the ratio d/A„. It will be seen later that over 
wider frequency ranges the reflection coefficient 
no longer depends solely on this ratio because 
the permeability in magnetic materials changes 
considerably with frequency. 

Equation (6) may be solved for a. Let 

T = = 7r + ^7i . (8) 

Expressing k in terms of its real and imaginary 
part and setting tan krd — l/<j> equation (6) 
yields 


<f)(yr tanh kid — 1) — ji + i [<fyyi tanh kid 
ct = 

<f){yr tanh kid + 1) — 7i + i [<^i tanh kid 

H- 7r — tanh kjd] ^ 

+ 7 r + tanh kid] 

Consider first the case that e and fx have the 
same phase angle so that yi = 0. Equation (9) 


\ SECRET^ 


109 


no 


THEORY AND APPLICATIONS OF RESONANT ABSORBENT LAYERS 


can then be written 

I tanh kid — 1)=^ + (7 — tanh kjdy 

^ 0^ (7 tanh kid 1)^ + (7 + tanh kid)‘^ 

7 — tanh kid 


arg 


a = tan~M ' 


0(7 tanh kid 


— tan“ 


uid n 

t 7 H" tanh kid 
0(7 tanh ki^ 


7 — tanh k^d 


1 - g 

7 -h tanh kid 


1+3 


where 


Q = 


tanh kid 


kjd = {2iU -|- 1 ) ~ 


0 , 1 , 


quarter wave layer of the same material. Let 
Xo, do, and Qo refer to the quarter wave layer 
while Xu du and gi refer to the three-quarter 
wave layer. Then 

^ m ^ tanh^ kida 

tanhA^i«i = tanh okido = tanh/^tdo : 


1 + Stanh^fc.do 


(18) 


. ( 11 ) 


Hence |a|2 has its minimum value, |an,in|, at 
0 = 0. At the minimum 


( 12 ) 


(13) 

(14) 


First suppose that 5 ^o>l, then since tanh Skido 
is necessarily greater than tanh kido it follows 

tanhSWo S + tanh^fc^do , 

= = ^0 1.0^ V.2 7 ^ 

7 1 -f 3 tanh^ kido 

In most cases (ktdo)^ 1 so that the standing 
wave ratio for the three-quarter wave layer is 
just three times as great as for the quarter 
wave layer. Hence it is always greater than 3. 
Next suppose go < ly then 


] 0 < 1 
arga„.„=j_^ 9 >r 

The conditions for complete absorption are 
therefore 


= Z 


1 3 + tanh^ kido 


a:o 1 -f- 3 tanh^ kido 


( 20 ) 


(15) 


tanhA^id = 7 g = 1. (16) 

It will be noted if the absorption is not com- 
plete, the phase of the reflected wave at the 
minimum is 0 or — tt. In the first case corre- 
sponding to a too small loss in the layer, the 
electric field has a loop at the surface of the 
layer. In the second case corresponding to a too 
large loss, it has a node at the surface. The 
voltage standing wave ratio x is given by 

X = g for g> 1 

x = Uorg<l. 

g 

Which form of equation (17) is applicable 
can be determined by measuring the phase of 
the reflected wave. Hence measurement of the 
standing wave ratio, the phase of the reflected 
wave and the frequency at resonance, fix the 
values of tanh kid/y and kr. 

Determination of the phase of the reflected 
wave is difficult in some experimental arrange- 
ments. An alternative method to indicate 
whether the loss of the material is greater or 
less than that for a matching layer (g — 1) is 
possible by comparing a quarter and three- 


If (kidoY < 1 , iCi will be equal to ^/Xo if Xq is 
less than 3, and equal to Xq/^ if o^o is greater 
than 3. 

It can therefore be concluded that if a;o<3 
and 0^1 >3, the loss in the material is greater 
than the matching loss while if a;o<3 and a:i<3, 
the loss is less than the matching loss. In the 
latter case the standing wave ratios become 
equal when the loss is such that tanh kido — 
\/3y. Finally if a;o>3, the loss is less than the 
matching loss if Xi<^Xo and greater if a;i>a;o. 

To examine the behavior near resonance it 
is necessary to know how 0 depends on the 
wavelength. If Ao is the resonant wavelength 
and a' is a nearby wavelength, let 



AX = X(j 

— Xo 


(21) 


AA^r = k’r 

-kr. 


(22) 

= k 

■(-f) 

= kr(^] 

1 

>- 1 > 

(23) 


Then 

In equation (23) use has been made of the fact 
that c and ft do not vary appreciably in the 
wavelength range AA. Then 
0 = cot k'r (I 

-.o.[, 2 . +!)(,- 1-;)] 5 
= tan|^(2ra + 1) . (24) 


THEORY OF RESONANT ABSORBING LAYERS 


111 


For every value of aa the corresponding value 
of <f) is readily determined from equations (21, 
22, 23). In fact in most cases of interest 1 
so that 

<t> = (2n + 1) • (25) 

Using equation (10) and the definition of g 
in equation (13) the power reflection coefficient 
lap can be written 


tally as well as g. Equation (29) can then be 
used to find y. 

In case yi ^ 0, it may be assumed small in all 
practical cases, or more precisely y? y^ so 
that |y| = yr. This is equivalent to assuming, 
except when e = /t that ef and < ^2 go 
that pi = er and |/i,| = It follows that C kl 
and |A;| = kr. Equations (18) and (19) become 

kr = ko ^ erfJLr (30) 


(26) 

' ' (0/7)M7^S + 1)^ + (1+!?)^ 

Since y and g are slowly changing functions of 
frequency, the wavelength dependence of |ap 
is essentially determined by <f)/y. In view of 
equations (8) and (25) 

(27) 

From this expression it is clear that in a layer 
of given material and with a given value of 
AA, <t>/y is three times as large for a three- 
quarter wave as for a quarter wave layer. 
Hence the band width of a three-quarter wave 
layer is smaller than that of a quarter layer. 
The precise ratio depends on the definition of 
band width because the absorption curves have 
different shapes and different minimum values 
in the two cases. By a similar argument the 
band width is in general smaller for larger 
values of larger for larger values of 

V/A. In most cases the term y^g can be neglected 
so that equation (26) becomes 


i<t>/yy + (9- ir 

H- (9^ + 1)^ 


(28) 


In the next section the manner in which this 
equation is used to determine /a is described. 

It is also possible to determine y from the 
shape of the absorption curve in another way. 
The points of inflection in the graph of as 
against cf> can be found by setting the second 
derivative of equation (10) equal to zero and 
solving the resulting equation for <^. The fol- 
lowing relation is obtained 


, I 7(1 4- g) 

' = db — 7= ■ 


/s 1 +■ 


(29) 


This value of <f> can be determined experimen- 



Now if fir = tanh kid/yry equation (9) may be 
rewritten without making any approximations 
as 


[<t> {ylg— 1) — jiV + 7r [<i>yi9 + 1 — 

[<^ (7r gr -h 1) — yJ2 + Jr + 1 + 

(32) 


arg a = 


tan~i 


' yr{<hig + 1 — 9^) 1 

.<i>{yl9 — I) — 7 * J 


— tan~^ 


r 7r(07t9^ 4- 1 + 9^) ~j ^ 33 ^ 

L 0(7^ 4- 1) — 7t J 


It is evident that the minimum value of ja p no 
longer occurs a,t <f> = 0. Setting {d/dcf>) |ap = 0, 
it is found to occur for values of <f> satisfying 


- = 0. 

7,(1 4-7 7^9^ ) I 4- y^y^g 

To the first order in y. 


7« 14-9^ 

4 fi(l - 7?) 


(34) 


Then if g is not close to 1, the terms in y^ are 
negligible and 



However, if g is nearly unity. 


k..l* = ^[(l-sr)’‘ + ^^]. (36) 

Consequently the minimum value of the power 
reflection coefficient can never be less than 
yl /87r . most purposes this is not a serious 

limitation as the reflection coefficient can be 
made smaller than 1/125 even though yi/yr = 
The resonant wavelength, defined as the value 


112 


THEORY AND APPLICATIONS OF RESONANT ABSORBENT LAYERS 


at which the reflection coefficient is a minimum, 
is now given by 


M = (2n + 1) - + - . (37) 

'2 4 3(1-7?) 


Usually equation (15) can be used to find ky. 
Equation (37) can then be used to obtain a more 
accurate value after yi has been determined. 

From equation (33) it is apparent that the 
phase of the reflected wave is no longer 0 or tt at 
= 0. Setting argo; equals to zero, equation (33) 
yields 


7 

1 - 7?S^ 


(38) 


A quantity which is immediately determined 
experimentally is the difference in wavelength 
between the resonance point and the point at 
which the phase of the reflected wave passes 
through 0 or tt. From equations (34) and (38) 
this difference is 


<t>p 0/n 



+ 


4^(1- 7?) J 


(39) 


If the resonant point is at shorter wavelength 
than the point of zero phase, yi is positive. If it 
is at longer wavelength, yi is negative. 

Examination of equation (33) at </> = 0 shows 
that the phase of the reflected wave is 0 or tt 
under exactly the same conditions as before. 
Hence equation (17) still applies whether yi is 
positive or negative and the ratio tanh kid/yr 
can be determined as before. In view of the above 
mentioned approximations this ratio is 



-^(2n+l)- 

yrkr 2 


= J-(- + -)(2n+l)l- (40) 

\ Mr \^r Mr/ 4 

Thus if yr and K are determined as before, 
thereby fixing €r and /v, equation (40) yields the 
value of ci/cr + Mi/Mr- Similarly 




\ €r VMr €r/ 


Thus equation (39) can be used to find fii/iiy — 

Ci/ €»•• 

The nature of the changes in these results 
when the incident wave is no longer normal can 
be seen without calculation. In materials of high 
refractive index the angle of refraction given 
by Snell’s law is small for all angles of incidence. 
Consequently, the path difference between the 
ray reflected at the front surface and the ray 
reflected by the metal backing is nearly indepen- 
dent of the angle of incidence. The resonant 
wavelength of the layer will therefore be nearly 
correctly given by equation (15). The requisite 
damping of the internal wave, however, will be 
altered because the reflection coefficient at the 
front surface depends on the angle of incidence 
as well as the polarization of the incident wave. 
If the reflection coefficient is higher, smaller at- 
tenuation of the internal ray is required to 
produce cancellation of the reflected and emer- 
gent rays. If it is lower, larger attenuation is 
required. Hence, equation (16) will be altered 
in such a way that tanh kid is smaller than y 
when the incident wave is polarized with its 
electric vector perpendicular to the plane of in- 
cidence and tanh kid is larger than y when the 
incident electric vector is in the plane of in- 
cidence. In the latter case the required attenua- 
tion is infinite at Brewster’s angle as the reflec- 
tion coefficient of the front surface vanishes for 
this angle and polarization. Brewster’s angle for 
materials of high refractive index is close to 
grazing incidence. 

As before let ; 2 : = 0 be the front surface of 
the HARP layer and ; 2 : = — d be the back surface 
at which there is a perfect metallic reflecting 
plane. Let the xz plane be the plane of incidence 
and let the direction cosines of the incident wave 
be —sin 6 and cos 0. The incident and reflected 
waves then contain the coordinates in the form 
Q-4Jc^xmue while the internal 

wave contains the coordinates in the form 
(e^V -j- a'e-*V) . These solutions are obtained 
from equations (15), (22-25), and (26-29) of 
Chapter 10. The boundary condition at ; 2 : = 0 
must hold over the entire xy plane. Therefore the 
exponential terms containing x must be identical 
for the two solutions. Hence 


(41) 


kx = ko sin 6 . 


(42) 


THEORY OF RESONANT ABSORBING LAYERS 


113 


Equations (25, 29) of Chapter 10 can now be 
written to give the propagation vector in the 
layer 



The second radical gives the correction to kg re- 
sulting from oblique incidence. For polarization 
perpendicular to the plane of incidence, equation 
(43), ei is usually so large that the correction is 
negligible. For polarization in the plane of in- 
cidence, equation (44), e, may be much smaller 
so that the correction is appreciable and gives 
rise to a shift in the resonant frequency as the 
angle of incidence is changed. 

For polarization perpendicular to the plane of 
incidence the solutions of Maxwell’s equations 
in the layer area 


E,= 

Ag-ik.^ + a'e-‘'‘“) , 

(45) 

Hg = 

— a'e -*'*=■") , 

(46) 


Mi^o 

Hg = 

— Ae-’*'* (e*‘" + a'e “*■'■■*') . 

(47) 


M2^’0 


The solutions in air are obtained by setting 
A = 1, = /CoSin^, kg = k^co^e, and = 

fX 2 = 1- Introducing the quantity ^ (z) 


replaced by kg as given in equation (43) ; the 
quantity y must be replaced by 


= 


COS d = COS 6 




sin^ d 

eiAi2 


(52) 


It is evident that the resonance condition, equa- 
tion (15), is unaltered while equation (16) re- 
quires that tanh kid be reduced by the factor 
cos 6. 

For the polarization in the plane of incidence, 
the solutions in the layer are : 


= Ae 


■ikxx (JkzZ 




(53) 


E. = - a'e"**-') , 

e^kg 


(54) 


H, 


kg 


(55) 


In air the solutions are obtained from equa- 
tions (53-55) by setting A == 1, =kQ sin B, 
kg = ko cos 6 and €i = €2 = 1- Introducing the 
quantity 





0>z> -d. 


(56) 


^(z) = —cos 6 


cos d + ae cos 6 
cos B — ae”'*®'' cos B 


z >0. 


(57) 


The boundary condition that C(—d) = 0 gives 


(58) 

The boundary condition at 2 ; = 0 becomes 



Mifco 

kg 


0>z>-d, 


(48) 


kg 1- 

eikoTTV^ 


— f (0) = cos B 


1 + a 
1 — a 


(59) 


f(^) = 


1 e ^*®^ cosB ae '^'®^ cos B 

cos B e"^®^ cos B — a cos B 


z>0. 


(49) 


The boundary conditions that ^( —d) = 0 gives 


(50) 

The boundary condition at 2 : = 0 becomes 


Hiko 1 — e _ 1 1 + a 

k, cos0 1-a' 


(51) 


Comparison of equation (51) with equation (6) 
shows that the previous discussion of resonant 
layers is applicable in its entirety provided the 
following substitutions are made: k must be 


Hence, for this polarization the previous discus- 
sion is also applicable provided that the follow- 
ing substitutions are made : k must be replaced 
by kg as given by equation (44) ; the quantity y 
must be replaced by 

Y = _L k (60) 

" €1 ko cos B cos B yj €1 yl €2 Ml 

It is evident that the resonance condition, 
equation (15), is substantially unaltered while 
equation (16) requires that tanh k^d be now in- 
creased by the factor 1/cos B, Brewster’s angle is 
determined from equation (59) by putting the 
exponential terms equal to zero (a' = 0) and 


114 


THEORY AND APPLICATIONS OF RESONANT ABSORBENT LAYERS 


setting the resulting expression for a equal to 
zero. It is thus found to be the angle at which 
7 1 , = 1 and is given by : 


tan 6 = 




€2 (ci — Ml) 
€2 Ml “ 1 


(60a) 


The resonance condition, equation (16) , requires 
tanh kid = 1 which can only be satisfied if the 
attenuation in the layer is infinite {kid = oo). 

It is instructive to compare the behavior of 
a given layer at a given angle of incidence for 
the two states of polarization. Consider first a 
layer which has a matching loss at normal in- 
cidence (tanh kid — y). The second radical in 
equations (43) and (44) gives a slight shift in 
the resonant wavelength of the layer, the shift 
for the perpendicular polarization being im- 
measurably small while that for the parallel 
polarization may be several per cent. Otherwise, 
the presence of this radical in the succeeding 
equations gives no measurable effect. Then from 
equations (52) and (60) 


It follows that 


7 COS B 7 II 


7 

COS 6 


(61) 


tanh kid 

g\l = = COSI9, 

7„ 


(62) 


- tanh hd 1 (63) 

7 X COS 6 

Consequently a;|| == x_i. Thus, at resonance, the 
reflected wave has the same amplitude but op- 
posite phase for the two states of polarization. 
The equality of the standing wave ratio for both 
states of polarization provides a convenient and 
sensitive method of testing a layer for the critical 
loss. 

Consider a layer in which the loss is not equal 
to the matching value. Then 


tanh kid 

g\\ = C0S<9 , 

7 

(64) 

tanh kid 
d± • 

7 cos 6 

(65) 


If tanh kid/y>l (loss exceeds the critical value 
for normal incidence), decreases as 0 in- 
creases, reaching the value 1 at 


cos 0 II = 


7 

tanh kid ’ 


(66) 


while Qa, increases in value. Thus the standing 
wave ratio approaches unity for the parallel 
polarization while it becomes larger for the per- 
pendicular polarization. Similarly if tanh kid/y 
<1, decreases as $ increases, reaching the 
value 1 at 


tanh kid 

cosdj_ = 

7 


(67) 


while g y increases. The standing wave ratio ap- 
proaches 1 for the perpendicular polarization 
while it becomes large for the parallel polariza- 
tion. This reversal of behavior for the two states 
of polarization supplies a very simple means of 
determining whether the loss in a given layer is 
too high or too low. It may be noted that 



tanh kid 
7 
7 

tanh kid 


if (9 < 0|| , 
if <9 < dj_. 


(68) 


The substitution of vn and yj. for y also affects 
the band widths at different angles of incidence. 
The right hand member of equation (27) is mul- 
tiplied by cos 6 for parallel polarization and by 
1/cos 0 for perpendicular polarization. Hence the 
band width increases in the former and decreases 
in the latter case as the angle of incidence is 
increased. As grazing incidence is approached, 
the band width becomes very great for parallel 
polarization and very small for perpendicular 
polarization. 

The application of the previous results to a 
coaxial line is immediate. Since the electromag- 
netic wave in a coaxial line is transverse, all the 
results for a resonant layer with the incident 
wave normal to the layer are valid here. 

In a waveguide of the usual type the electric 
field is transverse while the magnetic field has a 
longitudinal component. The solution may al- 
ways be considered as a sum of two waves mak- 
ing an angle 6 with the z axis where, equations 
(43-45, 47), 

sine = — . (69) 

koa 

In the treatment for oblique incidence the ampli- 
tude, a, of the reflected wave is independent of the 
sign of 0, Hence, the formula for a applies to any 
combination of the waves with 0 and with 


EXPERIMENTAL RESONANT LAYERS 


115 


—6. Therefore, the previous discussion for a 
resonant layer with polarization perpendicular 
to the plane of incidence and for the angle of 
incidence given by equation (69) is valid for a 
waveguide. 

2 EXPERIMENTAL RESONANT LAYERS 

Experimental data® has been obtained for a 
wide variety of HARP films from a wavelength 
of 1 cm to 2 m. The largest portion of the data 
has been in the wavelength region from 3 cm to 
13 cm. A great variety of materials have been 
tested including many binders, different types of 
metal flake and film produced by many different 
fabricating techniques. However the data on 
magnetic films is relatively meager because the 
pressure of other developments did not permit 
much diversion of effort to this phase of the work 
until the concluding months of the war. Before 
summarizing the experimental information, a 
brief description of the measuring apparatus is 
in order. 

Measurements on HARP films in open space 
have been successfully made in the microwave 
region. The equipment is in principle very 
simple. The output of a signal generator ener- 
gizes a highly directional antenna such as a 
parabolic reflector or a horn-type radiator. The 
radiation is reflected from a metal plate whose 
linear dimensions must be several wavelengths, 
into a second directional antenna. A receiver, fed 
from the second antenna, is so arranged that its 
output meter indicates the received energy. The 
sample to be tested which must be geometrically 
identical with the metal plate is substituted for 
the plate. The ratio of received energies gives 
directly the power reflection coefficient of the 
sample. 

In the actual equipment the signal generator 
is modulated at an audio frequency. The receiver 
consists of a bolometer, an audio-frequency 
amplifier and an indicating meter. The bolometer 
is preferably a “barratter,” i.e., a fine wire, which 
absorbs the high-frequency energy, connected 
in a simple bridge circuit. If care is taken that 
the audio-frequency amplifier is linear, the out- 
put meter readings are directly proportioned to 
the received energy. With the metal plate in place 

aThe experimental work for the HARP program was 
largely carried out by R. W. Wright. 


the gain of the amplifier is adjusted so that the 
output meter reads 100. Upon substitution of 
the sample, the meter reads directly the power 
reflection coefficient of the sample. If a crystal 
is used, care must be taken to select a crystal 
which gives a square law response at the power 
levels of interest or a calibration of the crystal 
must be made. 

The horn-type antenna indicator has been 
found most convenient, particularly when 
mounted on a circular arch. A platform at the 
center of the circle is used to support the samples 
and the metal reference plates. Care must be 
taken that the angles of incidence and reflection 
from the sample are exactly equal and that the 
plane of the sample is exactly perpendicular to 
the bisector of the incident and reflected direc- 
tions. Care must also be taken that the samples 
are perfectly flat. If small samples are being 
tested, absorbing screens should be placed over 
the portions of the pedestal supporting the 
sample which are illuminated by the incident 
radiation. With these precautions the above 
equipment has been successfully used at plants 
of the Du Pont Company to control the produc- 
tion of HARP materials. 

For measurements made in a closed space, a 
slotted section of waveguide or coaxial line is 
used. The sample is mounted at the end of the 
line against a metal shorting plug. Care must be 
taken that there are no air gaps in back of the 
sample or at the surfaces of the sample for which 
there is a normal component of the electric field. 
This is extremely difficult to avoid when the 
sample has a high refractive index (>30). The 
measurement of the reflection coefficient is made 
in the standard way. 

Typical behavior of HARP absorbers is shown 
in Figures 1 and 2. The first set of curves are 
for S-band samples, the second for X band. It 
will be observed that in the wide range of band 
widths represented the band width is roughly 
proportional to the thickness. The tabulated 
values of the refractive index are obtained from 
the resonant wavelength A.o by the relation, 

JV = ^ . (70) 

4a 

This equation follows immediately from equa- 
tion (15), (n = 0) when it is remembered the 
refractive index is defined as A = kr/k^ = \/ . 


116 


THEORY AND APPLICATIONS OF RESONANT ABSORBENT LAYERS 


To compare the experimental data with theory 
it is convenient to replot the absorption curve 
with u = Nax/X^ as abscissa. From equation 
(27) 

0 _ TT NAX _ TTU 

7 2 /XrXo 2)Ur 

Then equation (28) with g = 1 becomes 



The curve of this equation with fir = 1 is the 
solid curve in Figures 3 and 4. The points shown 
in Figure 3 are taken from the curves of Figure 
1 for S-band samples, while those in Figure 4 
are taken from Figure 2 for X-band samples. All 
the X-band samples follow the theoretical curve 



Figure 1. Absorption curves for typical S-band HARP 
samples. 



3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.3 3.9 4.0 

X IN CENTIMETERS 


Figure 2. Absorption curves for X-band HARP samples. 



Figure 3. Comparison of theoretical and experimental 
absorption curves for S-band HARP. 



2.0 W 0.5 0 0.5 1/) 1.5 ZJO 


NAX 

‘o 

Figure 4. Comparison of theoretical and experimental 
absorption curves for X-band HARP. 


closely. The S-band samples with the exception 
of sample No. 2027 also follow the theoretical 
curve. 

It will be observed that in equation (72) the 
effect of fir can be described as an expression of 
the u axis. The contraction required to make the 
curve for sample No. 2027 coincide with the 
theoretical curve is approximately 2. Hence this 
sample has a permeability of approximately 2. 
The metallic component in this sample was 
molybdenum Permalloy. 

In Figure 5 curves are shown for a series of 
samples made of the same pigment and same 
binder. The X- and S-band samples are identical 
except for thickness while the G-band (1.5 m) 
sample has a somewhat lowered pigment content 
in order to bring the layer closer to the critical 
loss. It will be noted that at 3 cm the permeability 
is unity. At 10 cm the permeability is slightly 
less than 2 as determined from the width of 
the resonance curve. This is accompanied by an 




EXPERIMENTAL RESONANT LAYERS 


117 



Figure 5. Comparison of magnetic HARP at widely 
different wavelengtlis. 


increase in the refractive index. The G-band 
sample 722-3 has a permeability between 5 and 
6 although the metallic concentration is lower. 
It is therefore clear that the metallic component 
which was a magnetic iron nickel alloy must 
have considerable permeability at 1.5 m which 
decreases with increasing frequency and reaches 
the value 1 between 3 and 10 cm. 

The comparison of a quarter and a three- 
quarter wave layer has been made experimen- 
tally for quarter wave layers close to the critical 
loss. If the loss was greater than the matching 
loss it was found that the three-quarter wave 
layer had a standing wave ratio greater than 
3, whereas, if the loss was less the standing 
wave ratio was less than 3 in agreement with 
the discussion in Section 11.1. The comparison 
has also been made by changing the wavelength 
instead of the film thickness by a factor 3. 
For nonmagnetic layers the three-quarter wave 
resonance point occurred at a wavelength three 
times as great to within 1 per cent. It follows 
that the real part of the dielectric constant varies 
by less than 2 per cent when the wavelength is 
changed by a factor 3. Indeed measurements of 
the dielectric constant of HARP materials at 
frequencies below a megacycle have given results 
substantially in agreement with microwave de- 
terminations. In magnetic materials the refrac- 
tive index varies considerably because of the 
changes in permeability with wavelength dis- 
cussed in the previous paragraph. The imagi- 
nary part of the dielectric constant also may 
change considerably with wavelength if the 
power factor of the binder is frequency-depend- 
ent or in a wavelength range for which the skin 


depth in the metallic component is approxi- 
mately equal to the thickness of an individual 
flake. By proper choice of both factors materials 
have been formulated in which the imaginary 
component of the dielectric constant is also sub- 
stantially independent of frequency over wide 
ranges. 

For a few compositions, studies have been 
made of the temperature variations in a and 
er over a temperature range from — 50 C to 70 C. 
For the lower temperatures there was no ap- 
preciable change in either ei or the resonant 
wavelength. For temperatures, however, above 
60 C there was a substantial increase in a while 
the resonant wavelength of the layer remained 
unchanged. Therefore, any expansion or con- 
traction in thickness was compensated by a cor- 
responding change in refractive index. The 
change in the loss perhaps arises from a temper- 
ature-sensitive power factor in one of the or- 
ganic components in the binder. 

The behavior of absorbing layers at different 
angles of incidence is shown in Figure 6. The 
power reflection coefficients there plotted are the 
minimum values obtained from the absorption 
curve at each angle of incidence. Sample 3287 
is close to a perfect match at normal incidence 
while sample 3265 has a loss much below the 
critical loss. For a perfectly matched sample, ac- 
cording to equations (62), (63), the minimum 
standing wave ratio at an incident angle 0 is 
1/cos 6. Thus for 6 = 60°, x = 2 and the cor- 
responding power reflection coefficient is 



0 10 20 30 40 50 60 70 80 90 100 

ANGLE OF INCIDENCE 


Figure 6. Mininjum reflection coefficients for various 
angles of incidence and polarizations. 


118 


THEORY AND APPLICATIONS OF RESONANT ABSORBENT LAYERS 


[ ( 2 — 1 )/ ( 24 - 1 ) ] 2 = 0.11 ill approximate agree- 
ment with the experimental value shown in the 
figure. For a sample with less than the critical 
loss equation (67) may be used. From the figure 
Sx, = 70° so that g = 0.34. As this must be the 
reciprocal of the standing wave ratio for the 
minimum refiection at normal incidence, the re- 
flected power at normal incidence is (1— 0.34) V 
(14- 0.34)2 — Q 26. The experimental value 
shown in the figure is 29 per cent. 

The resonant wavelengths for sample 3287 
are given in Table 1. 


Table 1. Resonant wavelengths for HARP sample 
3287 for various angles of incidence and polarizations. 


Angle of incidence 
(degrees) 

JL Polarization 
(cm) 

1 1 Polarization 
(cm) 

15 

3.22 

3.21 

30 

3.22 

3.20 

45 

3.22 

3.17 

60 

3.21 

3.16 


Because this sample had a refractive index of 
only 12 the minima were quite broad. Conse- 
quently the accuracy of the above values is not 
better than ±0.01 cm. Nevertheless a definite 
shift to shorter wavelength is shown by the 
parallel polarization. From equation (44) is 
smaller and therefore the wavelength in the 
layer is longer as 0 increases. Hence to reach the 
resonance point the free-space wavelength must 
be reduced. Expansion of the second radical in 
equation (44) gives the fractional decrease in 
wavelength as sin^ (9/2c2. The shift in Table 2 
indicates a longitudinal dielectric constant, eo, 
of the order of magnitude of 10. 

When the angles of incidence are close to graz- 
ing incidence the arrangement described at the 
beginning of this section can no longer be used 
because the direct radiation from one horn into 
the other becomes too great and the geometrical 
conditions too poorly defined. Measurements at 
grazing angles have been made by using large 
parabolas separated a distance of 30 ft or more. 
The arrangement in principle is exactly as before 
but the coupling between antennas has been re- 
duced and the geometrical definition of in- 
cident and reflected beam improved. A second 
method has sometimes been employed which 
shows directly how interference effects from 
reflections at grazing incidence may be elimi- 
nated with properly designed HARP. A horn 


with 2-in. by 6-in. aperture was mounted at the 
end of a metal plate 6 ft by 2 ft so that the center 
of its main lobe was directed parallel to the sur- 
face of the plate and parallel to its long side. The 
horn was excited with the electric vector parallel 
to the short dimension of the plate so the wave 
reflected from the metal plate was polarized per- 
pendicular to the plane of incidence. The center 
of the horn was 6 in. above the metal plate. The 
arrangement is in effect the microwave version 
of Lloyd's mirror. The antenna pattern of the 
assembly was taken with and without a HARP 
covering on the plate. The HARP was designed 
to have low loss and hence to be effective at large 
angles of incidence. The antenna patterns are 
plotted in Figure 7. The deep and regularly spaced 
minima for the metal reflecting plate shows that 
the amplitude of the wave reflected from the 
plate is nearly equal to the radiation from the 
horn at each angle. The maxima and minima 
occur at the angles to be expected in this arrange- 
ment for a wavelength of 3.2 cm. The reduction 
of these maxima and minima shows the effec- 



Figure 7. Effect of HARP at wide angles of incidence. 
(Lloyd’s mirror). 


EXPERIMENTAL RESONANT LAYERS 


119 



Figure 8. Resonant absorption wavelengths as a func- 
tion of the sample size. 


tiveness of HARP in reducing the reflection from 
the plate. The absorption is greatest at an angle 
of about 20° (angle of incidence = 70°) . It may 
be noted that for angles less than 20° for which 


DIFFRACTION PATTERN 



Figure 9. Comparison of the diffraction pattern about a 
HARP sample with that about a metal plate of the 
same size. (Perpendicular polarization.) 


is greater than one, the phase of the wave 
reflected from the HARP layer is the same as for 
the metal plate. However, for angles greater 
than 20° for which ^ j_ is less than one, the phase 
of the wave reflected from the HARP layer is 
opposite to that reflected from the metal plate. 
This is clearly evident in the reversal of max- 
imum and minimum at 25° and at 28°. It is en- 
tirely in accord with the discussion in Section 
12.4. 

In the measurement of these samples in a co- 
axial line the large effect of small air gaps be- 
tween the sample and metal wall has been men- 
tioned. A very similar phenomenon occurs if fine 
cuts are made across a HARP film. It is found as 
the spacing between the cuts is reduced the reso- 
nant wavelength shifts to shorter wavelengths 
corresponding to a smaller effective dielectric 
constant in the layer. That it is due to the small 
air gaps which the electric field traverses, is con- 


OIFFRACTION PATTERN 



Figure 10. Comparison of the diffraction pattern about 
a HARP sample with that about a metal plate of the 
same size. (Parallel polarization.) 


120 


THEORY AND APPLICATIONS OF RESONANT ABSORBENT LAYERS 


firmed when the cuts are made parallel to the 
electric vector of the incident wave. Thereupon 
they have a much reduced effect. In Figure 8 the 
shift in resonant wavelength is plotted for a 
series of samples ruled into squares of different 
sizes. It will be noted that when the squares be- 
come smaller than a wavelength on a side, the 
refractive index begins to drop very rapidly. It 
will also be observed that if a test plate is to give 
accurate results for the resonant wavelength of 
a layer, the dimensions parallel to the electric 
vector should exceed two wavelengths. 

In all the previous discussions the effect of a 
HARP film on the specularly reflected radiation 
has alone been considered. Because reflecting 
objects are in general not large compared to a 
wavelength in the microwave region, it is of 
interest to study the diffracted radiation. If the 
diffraction pattern around a metal plate is ex- 
amined experimentally, it is found that the 
secondary diffraction lobes are not altered in 
magnitude by covering the plate with high di- 
electric constant HARP. The only effect of the 
layer is to remove the principal diffraction lobe 
which in the limit of geometrical optics becomes 
the specularly reflected beam. However, if mate- 
rial of low refractive index and having some 
magnetic permeability is used, then some of the 
secondary lobes are also cut down in magnitude. 
Such experimental results are shown in Figures 
9 and 10. The three diffraction curves shown in 
each figure are for the metal plate, the metal 
plate covered with sample G 958-A which had a 
dielectric constant of approximately 2,500 and 
the metal plate covered with sample 3963 which 
had a dielectric constant of approximately 30. 
These results indicate that it may be possible to 
formulate a material which substantially re- 
duces certain parts of the diffracted radiation as 
well as that specularly reflected. 

It has already been remarked that HARP ma- 
terial which is, isotropic in the plane of the layer 
is required in most applications. The techniques 
for producing nondirectional films have been 
described in the previous chapter. In Figure 11 
the absorption curves for a directional film 
formed by a succession of knifed layers are 
plotted. In this film the direction of the knife 
stroke was the same for each layer in contrast to 
the 90° rotation employed in fabricating nondi- 


rectional films. The curves show that the refrac- 
tive index is 13 per cent greater when the electric 
vector is parallel to the direction of the knife 
stroke. In some films the difference in refractive 
indices has been as high as 20 per cent. Conse- 
quently films can be produced in which this dif- 
ference is anywhere in the range from 0 to 20 
per cent. 

If a wave whose electric vector makes an angle 
6 with the directional axis is incident on a direc- 
tional film, it may be regarded as the sum of two 
waves with the electric vector parallel and per- 
pendicular to the axis. The relative amplitudes 
are cos </> and sin </> respectively. Each wave may 
be considered separately and the resultant ob- 
tained by vector addition of the two amplitudes. 
If the frequency of the incident radiation coin- 
cides with one of the resonance frequencies, that 
component will be absorbed and the other com- 
ponent alone will be reflected. The reflected wave 
will thus be linearly polarized perpendicular to 
the resonant axis. If a circular plate were cov- 
ered with this material and were rotated about 
an axis perpendicular to the plate, the amplitude 
of the reflected wave would be 100 per cent mod- 



Figure 11 . Resonant absorption of different incident 
polarizations for a directional HARP sample. 


EXPERIMENTAL RESONANT LAYERS 


121 


ulated with twice the frequency of rotation. The 
direction of polarization would go through a 
cycle making angles from —90° to 90° and back 
to —90° with the incident polarization direction, 
one cycle being made for each revolution. When 
the absorption of the sample is not complete, ac- 
count must be taken of the phase changes near 
resonance. Since the component on the resonance 
axis may be shifted in phase by a large amount, 
the resultant reflected wave will be elliptically 
polarized. Thus directional HARP material may 
be used to produce a variety of polarization ef- 
fects. 

In some applications it is necessary to remove 
reflections from curved surfaces. The effects of 
curvature on a resonant layer are easily ex- 
amined experimentally by studying the reflection 
from long cylinders of different radii. The re- 
sults for two Aims, one of high and one of low 
refractive index, are shown in Table 2. The 
resonant wavelengths and minimum reflection 
coefficients for polarization of the incident elec- 
tric vector parallel and perpendicular to the 
length of the cylinder are given. The values are 
obtained from complete absorption curves in 
which the reflections from the covered and 
metallic cylinders were compared at each wave- 
length. 


Table 2. The effect of curvature on a resonant layer. 
Newburgh Sample {N = 50) 


Radius of 
curvature 
(inches) 

Parallel 

polarization 

Minimum 
Ao reflection 

(cm) (percent) 

Perpendicular 

polarization 

Minimum 
Ao reflection 

(cm) (percent) 

00 

9.75 

2 

9.75 

2 

1^ 

9.6 

2 

9.4 

6 

1* 

9.55 

4 

9.5 

12 

h 

9.4 

8 

8.9 

25 


Sample 2036 {N 

= 10) 



Parallel 

Perpendicular 


polarization 

polarization 

Radius of 


Minimum 


Minimum 

curvature 

Xo 

reflection 

Xo 

reflection 

00 

10.7 

4 

10.7 

4 

1 

10.8 

7 

10.6 

6 


*Absorption curves for this radius show some peculiarities probably 
because the diameter of the cylinder is exactly a half wavelength. 


It will be noted that when the electric vector 


is parallel to the axis of the cylinder there is 
no appreciable change in the behavior of the 
absorber until the curvature is reduced to a 
small fraction of a wavelength. With perpen- 
dicular polarization an appreciable shift in res- 
onant wavelength appears when the radius of 
the curvature is a half wavelength. For radii of 
curvature less than one-quarter of a wavelength 
there is a substantial increase in the minimum 
reflection. To compensate the difference for the 
two polarizations, directional HARP may be 
used with the direction of low refractive index 
parallel to the cylinder. The fabricating proc- 
esses which give directional films have been pre- 
viously discussed. The required directionality 
may also be achieved by a series of fine cuts into 
the layer which should be perpendicular to the 
axis of the material (cf. previous discussion). 
Whenever the thickness of the layer is unimpor- 
tant, a film of sufficient band width that the shift 
in resonant wavelength is less than the band 
width may be used. It is probable that the min- 
imum reflection coefficient for small radii of 
curvature could be improved by increasing the 
loss in the film. 

Transmission Filters 

The possibility of using a half-wave film of 
high dielectric constant material for a selective 
transmission filter has been mentioned in Section 
9.1.1. In this section a detailed examination of 
the transmission and reflection characteristics 
of such filters is made. Their behavior in open 
space is first considered. The changes brought 
about when the films are used in a coaxial line 
or waveguide are then indicated. 

Let .e = 0 be the front surface and z = — d be 
the back surface of the HARP film. If the in- 
cident wave is normal to the xy plane, the previ- 
ous expressions for the electromagnetic field in 
the region z > —d are valid. In particular, equa- 
tions (3) and (4) still obtain. In the region 
z < —d the field consists of a transmitted wave 


E = 

(73) 

U = H,= - 

(74) 

Correspondingly 


1 

VI 

1 

II 

S 

(75) 


122 


THEORY AND APPLICATIONS OF RESONANT ABSORBENT LAYERS 


The continuity oi ^(z) 2 ii z = ^ and z = —d re- 
quires that 


1 + ^ 
1 — a 


-r(o) = 7 


l + a' 
I- a’’ 


(76) 


1 + 
7 1 _ 


= -r(-d) = 1- 


(77) 


The conditions for the continuity of the tangen- 
tial electric field, which will also be needed, are 


l + oc = A{l + a'), (78) 

l3e-''‘ “ = A (6-*“ -I- aV“) . (79) 

The solution of equations (76-79) for the re- 
flection and transmission coefficients, a and /3, are 


a = (y - 1) 


pikd p—ikd 


(1 + 7)2 — (1 — 7 )^ 



(1+7)2 ~ (1 — 7)2 6-**^ 


(80) 

(81) 


A noteworthy result follows from these equa- 
tions for a very thin film, (kd)^^ 1. Equation 
(80) becomes 


i{y^ - DM 
iiy^ + l)kd + 27 ’ 


(82) 


Here, as in the remainder of this section, 1 
in all cases of interest. Expressing 7 and k in 
terms of e and fi 

^ - 1 

^ i\o (83) 



Hence, for very thin films the power reflection 
coefficient is proportional to rather than to 
ed^. Consequently metal films much thinner than 
a skin depth will reflect a large portion of the 
incident energy. For example, at 10 cm the skin 
depth of Cu is about lO-^ cm. Nevertheless, a 
film 10“’^ cm in thickness (e = = 3.4 X 10~®) 

will reflect 80 per cent of the incident energy. 
Similarly a HARP film with c,. = 2,000 which is 
1 mil thick will reflect 70 per cent of the incident 
energy. 

In filters high selectivity and high transmis- 
sion are desirable features. Hence, materials 


with small loss and as high refractive index as 
is consistent with a small loss are used. For these 
films (kid)^ is always negligible in comparison 
with 1 and nonmagnetic materials are always 
used. Expressing k in terms of its real and imag- 
inary parts and setting 4> = tan krd, equations 
(80) and (81) can be written in this approxima- 
tion as 


13= - 
|«| 2 = 1 - 


g + i <f>/2y ^ 

l-\-g + i <t>/2y ' 

l + 2g 

(1 + gy + i<f>/2yy 
1 1 


cos krd 1 + gf + i<f)/2y 
1 1 


cos 2 krd (1 + gy + {<f>/2yy 


(85) 

( 86 ) 

(87) 

( 88 ) 


The abbreviation g = kid/2y has been intro- 
duced. These equations show maximum trans- 
mission of (1 + ^)~2 and minimum reflection of 
5 ^ 2(1 + ^) - 2 . Both occur at = 0. The quantity 
25 r (1 + ^)-2 is the energy dissipated in the film. 
The condition that </> = 0 is 


krd = mr n = 1, 2, • • • . (89) 

Thus the quantity g is 



(90) 


Hence for a half wave filter, g is identical with 
the g for a quarter wave absorber of the same 
material. Refer to equations (13) and (15). It is 
interesting to note that material w+ich is perfect 
for an absorber {g = 1), will transmit 25 per 
cent, reflect 25 per cent and absorb 50 per cent of 
the incident energy when it is used as a half- 
wave filter. 

The wavelength dependence of the transmis- 
sion is principally determined by <^, the term 
l/cos 2 krd changing only slightly over the region 
of transmission. If AA is defined as in equation 
( 21 ), then 


27 27 L \ Xo/J 27X0 

= -!^^Ve. (91) 

2 Xo 

For a half-wave filter, this is precisely the same 
quantity that governed the wavelength behavior 




EXPERIMENTAL RESONANT LAYERS 


123 


for a quarter wave absorber, equation (27). 
Equation (88) can now be written as 


1 

1 

(1 + < 7 )^ 

1 + 

- “12 
TIT AX V € 

_2X„ (1 + g)_ 


(92) 


The transmission as a function of wavelength is 
thus a typical resonance curve. The half width 
at the half-power point is 


^ . (93) 

Xo mryje 

Next suppose that the angle of incidence is 6 
and the electric vector is perpendicular to the 
plane of incidence. Equations (45-47) describe 
the field in the region z > —d and equations (48, 
49) remain valid. For the region z < —d the 
equations for the field will be the same as in the 
region z > 0 except that a must be set equal to 
zero and all the field components must be mul- 
tiplied by 

f («) = z<-d. (94) 

COS d 


The continuity of ^{z) at 2 : = 0 and z = —d 
requires 


1 1 -|- q: /xi^o \ a' 

COS 6 1 — a kz I — a' 


(95) 


/Xi/Co \ Ot 6 1 

17 


(96) 


The continuity of the tangential electric field 
gives 


1 + « = A (1 + a') , (97) 

A ' . (98) 

Comparison with equations (76-79) shows 
that the previous results apply provided that k 
is replaced by of equation (43) and y is re- 
placed by yj. of equation (52). The first change 
has no effect because the difference between kg 
and k is negligible. The second requires that y 
and g be replaced by 


7j_ = 7C0S^ (99) 

= ( 100 ) 

COS 6 

Hence, with increasing angles of incidence, the 
maximum transmission diminishes whereas the 
band width of the filter becomes smaller. 


When the electric vector lies in the plane of 
incidence, equations (54) and (55) describe the 
field in the region z > —d and equations (58) 
and (59) remain valid. For the region z < —d 
the components of the field will be given by the 
same equations as in the region z > 0 except 
that (X must be set equal to zero and each field 
component multiplied by Then 


^(z) = —cosd z<—d. (101) 

The continuity of ^{z) at z = 0 and z = —d 
requires 


— cos 


1 + QJ 

1 — q: 


kz \ (x! 

€iko \ — a' 


( 102 ) 


^ 1 -I- 

1 - a'e"’*-" 


COS0 . 


(103) 


The continuity of the tangential electric field 
gives equations (97) and (98). Comparison with 
equations (76-79) shows that the results for 
normal incidence also hold here if k is replaced 
by k. of equation (44) and y is replaced by yu 
of equation (60). The first change may now 
have some effect on the resonant wavelength 
but is otherwise negligible. The second gives in 
place of y and g 



(104) 


gr„ = gfcosi?. (105) 

Hence, with increasing angles of incidence the 
maximum transmission improves while the 
band width of the filter becomes larger. 

In Figure 12 the experimentally measured 



545 

X IN CENTIMETERS 


P^iGURE 12. Transmission of a HARP filter as a function 
of wavelength for various angles of incidence. 


124 


THEORY AND APPLICATIONS OF RESONANT ABSORBENT LAYERS 


transmission of a HARP filter is shown. The 
transmission was found by inserting a screen 
of the material two feet square between the 
transmitter and receiver antenna. These an- 
tennas are highly directive horns placed about 
six feet apart and pointing directly at each 
other. The ratio of received energy with and 
without the filter in place gave the power trans- 
mission coefficient. Care must be taken to avoid 
reflections from the filter into the transmitting 
horn by placing the screen at a sufficient angle 
with the line joining the horns. The presence 
of such reflections can be immediately recog- 
nized for the transmission of the screen then 
depends on its position between the horns. It 
was found that the angle of incidence on the 
screen could not be made less than 30° on this 
account. 

The material of the filter had a refractive 
index of 13. As the maximum trans mis sion is 
two-thirds at 30° incidence, g = ^Z/2 — 1 = 
0.22 and the theoretical half width according to 
equation (99) is (2 X 1.22)/ (3.14 X 13) = 0.060. 
The experimental value of AA/AisO.2/3.2 = 0.063. 
The polarization used was perpendicular to the 
plane of incidence. Then at 60°, g should be 
0.22 (cos 30°/cos 60°) = 0.38 and the corre- 
sponding maximum transmission is 52 per cent 
in good agreement with the experimental value 
shown in the figure. The decreased band width 
required by equation (99) is also quite evident 
at the larger angles of incidence. 

The results obtained for normal incidence can 
be applied without change to a filter in a co- 
axial line just as in the case of an absorbing 
layer. Likewise the results for polarization 
perpendicular to the plane of incidence at angle 
of incidence given by equation (69) may be 
used to describe the behavior of a filter in the 
usual type of waveguide. 

Composite Layers 

Throughout the previous discussion it has 
been assumed that the absorbing medium is 
homogeneous. In this section the extension to 
inhomogeneous or composite layers is treated. 
A number of special problems which have 
arisen in the course of the development of 
HARP materials will be considered. These in- 
clude the behavior of an absorber when a thin 


layer of low dielectric constant is inserted be- 
tween the metal backing plate and the medium ; 
the cross lamination of directional HARP to 
produce a nondirectional film; the behavior of 
a striated medium composed of alternate layers 
which are thin compared to the internal wave- 
length. 

Suppose the medium consists of P layers 
separately designated by an index n which can 
have the values 0, 1, • • • P. The index 0 desig- 
nates the air space which shall be to the right 
of the plane z = ^. Let the bounding plane be- 
tween the nt\i and + 1 layer he z = —In. The 
thickness, d„, of the nih. layer is then given by 

dn = In — In - 1- (106) 

The total thickness d of the medium is 


p 

= (107) 

1 

The electric and magnetic fields in the nih 
layer are given in equations (1) and (2) if 
the subscript n is affixed to the quantities A, k, 
a', €, and /x. The expression for ^{z) is 


U{z) = 




The boundary conditions are that 


In ^ Z ^ ln-1 • 

(108) 


U (- In-l) = ^n-1 ( - In-l) 71=1,2 •••P. (109) 


In this set of equations + the value 

of ^ at the metal reffector, has been defined to 
be zero. As the value of is fixed in terms 
of a' by equation (110), successive application 
of this recurrence relation will determine a' in 
terms of a^'. 

It is convenient to use a compact notation in 
eq uatio n (110). If y„ is introduced in place of 
\/fjin/e„, it follows that 




1 + anC 


”1 




( 110 ) 


= (111) 

1 — CKn 

where 

(Xn = OLnC^ ''” " . ( 112 ) 

It will be observed that ^ is a linear fraction in a 


EXPERIMENTAL RESONANT LAYERS 


125 


of the type a + 6a/c + da. Let the operator T 
be defined as 

a ha 


Ta = 


c da 


(113) 


It may be represented as a square array of the 
four coefficients a, b, c, and d. Thus 


■[: ;] 


(114) 


The first column contains the coefficients of the 
numerator and the second column contains the 
coefficients of the denominator. The first row 
contains the coefficients of a while the second 
line contains the terms independent of a. Since 
Ta is a linear fraction, it is obvious that if each 
element in equation (114) is multiplied by a 
common factor, Ta is unchanged. Likewise a 
common factor may be taken from the first 
column if Ta is multiplied by this factor and a 
common factor can be taken from the second 
column if Ta is divided by this factor. The ad- 
vantage of using the above notation appears 
when a succession of two or more operations 
are considered. By definition, equation (113), 


T^iT.a) 


02 + h2 (oi + b]a) / (ci + dia) 
C2 + ^2 (oi + hia) / (ci + dia) 
O 162 "h C 1 Q 2 “h (^ 1^2 “b diQ^a 


01^2 + C 1 C 2 + (hid2 + diC2)a! 

If the coefficients of the fraction in equation 
(115) are compared with coefficients in the 
square array of the matrix product T 1 T 2 , they 
are found to be identical. Hence 

T2(T,a) = T.T^a. (116) 

where T 1 T 2 is the matrix product of Ti and To. 
Equations (110, 111) can now be rewritten as 


= Vnan. 
^«(“" W = UnCXn. 


(117) 

(118) 


where 

V. 


-L; . J 


. (119) 


Tn-1 

iTn IJ 

The reciprocal of JJn which will be needed later is 


r 1 1 

U-n^ = \ 

L-t„ 7 J 


(120) 


for 

U:, 


L-y„ U 

_r 2 yn 0 in ol 

~ Lo 2y.i ~ [o ij 


Equation (109) becomes 

~ hi n—ian—1 OF Q^n— 1 ~ ^ nU n-l (121) 

Let Wn be defined as 


W 


„=t/;'F„=r ^ 

L-7n 7nJL7n 


^-2lkndn~ 


where 


Jifi 


[_ynhn 1 J 

(122) 

tdn __ ^ikndn 


,dn ^-ikndn ~ tauh ikndn • 

(123) 


The solution of equation (121) for ao is therefore 

a„ = FpL7-i Fp_, • • • t/r.‘ F„ • • • t/l'F, f/o'ap 

= UpWp • • • TF„ • • • WiU'o'ap . (124) 

From equation (109) with n = P + 1, it follows 
that ap = —1. Now 


Upap = l’’ ^ (-1) = 0. 

Ltp ij 


(125) 


Hence, equation (124) may be rewritten as 

«o= Tfp •••TriC/o"'(0). (126) 

Consider first the application of equation 
(126) to a homogeneous layer. Then 


«0 


p yr^hl r 1 l1 

Lti^i 1 J L-l iJ 

[ 


( 0 ) 


(127) 


1 1 
-1 1 


(7iW= (128) 


yihi + 1 

Precisely the same result is obtained by solving 
equation (6) for a. 

Next suppose the layer consists of two parts. 
Then 


p --Mr "1 

lyji, 1 J lyih 1 J L-l iJ 

r 1 — 1 + 7 i~'iii 1 

= (y^hn) 

|_7iAi — 1 yihi +1 J 

yihi -|- 72^2 — 1 — 7i~^ y^^hi 

yihi 72^2 + 1 "h 7i~^ y^hih. 


( 0 ) 


(129) 

(130) 


126 


THEORY AND APPLICATIONS OF RESONANT ABSORBENT LAYERS 


If h' and k[ are defined by the relation 
2 2 '' 


Jh = tanh ik 2 d 2 = — , (131) 

Ti 

equation (130) can be rewritten as 


do 


hi + h2 
1 hih2 
^ hi-\- h2 
1 + hih2 


yih — 1 

jih + 1 


(132) 


By virtue of the addition law for hyperbolic tan- 
gents 

h = tanh i(kidi + k 2 d 2 ) . (133) 


In the first application of equation (133) , sup- 
pose d 2 is sufficiently small that (^ 2 )^ 1* 

Then 


'^h,= ik^ = ik^^ p = iki(k - . (134) 

Tl 'V Mi€2 'V 

Hence 

ki = ki'^ (135) 

Ml 

and 

h = tanh + — ^ 2 ^ J • (136) 

Equation (136) shows that with the interposi- 
tion of a thin layer between HARP and the metal 
plate, the unit behaves as a homogeneous layer 
with a propagation constant 1 x 2 ^ 2 / d^) / 

(d + dg)]- For a nonmagnetic substance the 
thin layer therefore increases the thickness of 
the film just as though the added material had the 
same dielectric constant as the rest of layer. The 
following table shows the experimental results 
when adhesive layers of different thicknesses are 
placed between a HARP film and the metal back- 
ing plate. It will be observed that th5 resonant 


Table 3. Effect of adhesive layers of different 
thicknesses placed between a HARP film and the 
metal backing plate. 


Thickness of 
adhesive in 
mils 

Total film 
thickness, d, 
in mils 

W avelength 

Xo in cm 

Xo 

4d 

0.0 

19.8 

8.66 

43.1 

1.5 

21.3 

9.22 

42.6 

3.9 

23.7 

10.20 

42.4 

4.7 

24.6 

10.65 

42.7 


wavelength is proportional to the total film thick- 
ness. Consequently the effective propagation 
constant for the whole layer is unchanged as 
paper is added. The complete absorption curves 
show that the value of the minimum reflection is 
also unchanged as paper is added. In the ap- 
plication of HARP film to a metal backing plate 
this result must be kept in mind, for a thin layer 
of adhesive adds to the total thickness of the 
HARP film just as if it also had a high dielectric 
constant. 

In the second application of equation (133) 
suppose the two materials have nearly identical 
electromagnetic properties. Let 


72 = 7i 4" ^7 = 7 + ^7 j (137) 

/r' = k2 + Ak' = k + Ak + Ak' , (138) 

k2 = k Ak . (139) 

Equation (131) gives 

h 2 = tanh ik 2 d 2 + iAk' d 2 (1 — tanh^ ik 2 d 2 ) 

= ^1 + tanh ik 2 d 2 . (140) 

Hence 


Ay . Ay 

iAk'd 2 = — sinh 2ik2d2 = — i sin2M2. (141) 
27 27 

It has already been mentioned that certain 
processes for the production of HARP give di- 
rectional materials. By laminating two layers 
at right angles it is possible to construct a non- 
directional film. Let ki^yi refer to one axis and 
/C 2 ,y 2 refer to the perpendicular axis of the mate- 
rial. Equation (140) may be applied to deter- 
mine the ratio of thickness required to effect 
this result. The imaginary parts of k and 7 can 
be neglected. Then for one polarization of the 
incident wave 

arg h = \k 1 d 2 + ^^ 2^2 = kd + ^2 ( AA: + sin 2kd^ . 

\ 2yd2 / 

(142) 

In the other polarization the material constants 
ki,yi and /C 2 ,y 2 are interchanged. Hence 

/ ( Ay \ 

arg h' = Ml + kid 2 — kd + I AA; sin 2kd2 1 . 

\ 2ydi / 

(143) 

If the layer is to behave in the same way for both 
polarizations, arg h must be equal to arg h'. 


EXPERIMENTAL RESONANT LAYERS 


127 


Hence 


Ak(di— c?2) = — sin2/;;c?2. (144) 

T 

Equation (144) will be applied to nonmagnetic 
HARP for which fi = 1. Then 


A 7 

7 


1^ 

2 € 


and 


Equation (144) becomes 


Ak 1 Ae 

T "" 27* 


(145) 


k{dk— di) = sin 2kd2. (146) 

Since the layer is supposed a quarter wave ab- 
sorber 


m + <k)=l- (147) 

The numerical solution of equations (146, 147) 
yields 

kd2 = 66° kdi = 24° 


di 

di di 


0.27. 


(148) 


In the following table, the experimental results 
for films constructed of eight directional layers 
are shown, x h and x ± are the resonant absorption 
wavelengths for the two polarization states. 


Then 

WnW, 


/ f” ^ ^ kodfi 1 

kodfi 1 _ _i€fikodfi 1 _J 

Pi kodfi dfi ikoi^iifi dfi “|“ M/^d;^)”l 

~ -7 / " 7" I ' i' \ " '72 7" 7' ■ 

[Jlkoi^ndfi “T ^ndfi) 1 t^nkodfi dfi_\ 


If Jlfi and ~€n are defined as 

_ f^n dfi ~r Mn^n j 

dfi “T d.fi 

" y 4_ 'a' 

dfi 1“ ^fidfi 

4 + d'fi 

equation (130) can be rewritten as 

'^J^nkodn 

IP n IP n ~ I 

{ykjJCodn 1 

where d, = d!' + 


(154) 

(155) 

(156) 


The corrections to the diagonal elements have 
been neglected as their effect can be shown to be 
small. Therefore the pair behaves as a single 
layer characterized by the constants and Jin 
and having a thickness d„. 


Table 4. Resonant absorption wavelengths for nondirectional HARP 


di in mils 

d 2 in mils 

di/(di + di) 

X|| in cm 

Xj_ in cm 

^11 — Xx in cm 

0 

168 

0.00 

11.0 

9.6 

1.6 

21 

147 

0.13 

10.6 

9.95 

0.65 

42 

126 

0.25 

10.25 

10.35 

-0.1 

63 

105 

0.38 

10.1 

10.75 

-0.65 


It will be noted that the resonant wavelengths 
for the two polarizations become equal at ap- 
proximately the value of di/(di + ^ 2 ) predicted 
by equation (148). 

The treatment of many layers which may be 
grouped in pairs and which are all thin will next 
be considered. Let e', dl, k'„, yl refer to one 
member of the nth pair while d", k” and y" 
refer to the other. Since {k[d'„y and {k"d”y are 
small compared with unity 


" 7 " l/^n -7 " j" • " 7 j" 

InK = — '^k,n dfi = lUfi Kodn , 

\ 

(149) 

= J^.ikndn = 7 ,' 

(150) 

\ M77 


y'fihfi = ifinkodn , 

(151) 

yrT^hn = i^kod'n . 

(152) 


The result may be applied to a medium con- 
structed of alternate dielectric and conducting 
layers. It shows that each unit comprising a 
dielectric space and a conducting layer acts as 
though it had a conductance of ad'/d where 
or is the conductivity of the conducting layer and 
d' is its thickness. An absorber based on the idea 
of gradually increasing conductivity as the layer 
is entered could therefore be made of regularly 
spaced sheets of increasing conductivity or of 
sheets with low conductivity spaced a decreasing 
distance apart. 

Equation (156) may also be applied to an ar- 
rangement of alternately spaced high and low 
dielectric constant materials. If the dielectric 
constant of one of the substances is negligibly 
small, as is the case when thin HARP films are 
interleaved with paper, and if ix = 1, the effec- 


128 


THEORY AND APPLICATIONS OF RESONANT ABSORBENT LAYERS 


tive dielectric constant of a unit is simply 
€{d'/d) where d' is the thickness of the HARP 
film and d the total thickness of the unit. If the 
unit is repetitive, e{d'/d) is the effective dielec- 
tric constant of the medium. It will be noted that 
both the real and imaginary parts of c are re- 
duced in the same ratio. From equation (17) the 
standing wave ratio at the resonant point of the 
film is 

tanh Ic id 7r€j 

x = g = = — (157) 

y 4Vc 

Hence, if the HARP film has too high ci for a 
perfect match, g > 1, the interleaving of paper 
will lower the minimum reflection until a perfect 
match is reached because ej decreases more 
rapidly than In fact if Xi is the minimum 
standing wave ratio for the HARP film alone 
and X that for a diluted medium, then 



Hence a perfect match should be reached when 


The following table shows the experimental 
results for thin HARP films interleaved with 
paper. The films had been prepared on thin sheets 
of paper so that no measurements were made on 
an undiluted HARP film. 

It will be observed that N^d/di is very nearly 
constant as should be the case if the propagation 
constant is proportional to \/di/d. There are 
some irregularities in the standing wave ratio. 
If it is assumed that the last row of the table 
corresponds to a perfect match, the standing 
wave ratios, according to equation (158), should 
be 2.45/2.10 = 1.17 for the third row, 2.45/1.82 
= 1.35 for the second row, and 2.45/1.47 = 1.68 
for the first row. The difficulty probably is the 
result of inaccuracies in the measurement of the 
standing wave ratios. 


Table 5. Reflection from thin HARP films interleaved with paper. 


No. of paper 
backed HARP 
samples 

No. of added 
paper sheets 
between 
each sample 

Total 
thickness 
in mils 

HARP 
thickness 
in mils 

Vd/di 

s.w.r. 

Energy 
reflected 
(per cent) 

N = Xo/4d 

NVd/di 

13 

0 

82 

38 

1.47 

2.62 

20. 

12.0 

17.6 

11 

1 

110 

33 

1.82 

1.57 

0.5 

9.0 

16.4 

10 

2 

128 

29 

2.10 

1.15 

0.5 

7.6 

16.0 

9 

3 

150 

25 

2.45 

1.15 

0.5 

6.6 

16.2 


Chapter 12 

TECHNICAL APPLICATIONS OF HARP 


12 1 USES OF HARP 

T he high dielectric constants and permea- 
bilities that are available in HARP materials 
open a number of new possibilities in the field of 
electronics. Not only are high dielectric constant 
and high permeability in themselves useful, but 
also there are probably associated properties 
which have not been investigated and which 
may lead to technical applications. The studies 
made to the present have been exclusively de- 
voted to radar applications, largely in the micro- 
wave region. They are the subject of this chap- 
ter. Such applications are by no means repre- 
sentative of the possible uses for HARP. 

Radar applications can be divided into two 
classes. The first class comprises systems which 
are primarily based on the properties of HARP. 
Two kinds will be discussed, namely, systems of 
radar camouflage using absorbent HARP lay- 
ers, and identification systems based upon reso- 
nance and polarization characteristics of HARP 
films. These are the subjects of Sections 12.2 
and 12.3. In the second class belong the many 
uses of HARP absorbers in improving the per- 
formance of radar systems and in making labo- 
ratory tests. They are the subjects of the re- 
maining sections of this chapter. In Section 
12.4 the removal of undesired reflections in 
specific radar installations is discussed. The pos- 
sibilities of using HARP for screening and while 
tuning up a radar system are considered in 
Section 12.5. The concluding section deals with 
terminations and the laboratory uses of HARP. 

122 CAMOUFLAGE 

Of the many ways to confuse and interrupt 
enemy radar operation, the camouflage of a 
target by absorbent materials so that it becomes 
invisible is, in principle, the simplest and most 
effective means. Certain difficulties appear, 
however, when the factors governing the 
strength of the return radar echo are considered 
in detail. 

A radar target in most cases can be charac- 


terized by a cross section a which is defined as 
the ratio of energy per unit solid angle scattered 
backward to the incident flux of energy. It has 
the dimensions of length squared. It is deter- 
mined by the nature of the target and, for tar- 
gets large compared to a wavelength, varies 
rapidly as a function of the target orientation. 
The strength of a radar echo is proportional to 
the target cross section. It also depends on the 
intervening medium and on the characteristics 
of the radar set. For a given radar set the 
strength of the echo from an isolated target is 
proportional to the fourth power of the distance 
to the target. Hence for an isolated target the 
cross section must be reduced by a factor of 
2^ = 16 if the maximum range at which the 
target can be detected is to be halved. For tar- 
gets over smooth water, which is virtually a 
metallic reflector, the echo strength may vary 
as higher power of the distance because can- 
cellation of the directly scattered radiation by 
the radiation reflected from the water takes 
place. At large distances, for surface search, the 
strength of the echo varies inversely as the 
eighth power of the target distance. In such a 
case the reduction of the cross section required 
to halve the range is a factor 2® = 256. There- 
fore, very large reductions in cross section are 
necessary to change the radar visibility of a 
target by a significant amount. 

Except in rare instances a target is a large 
and complex structure. The incident radiation 
is returned from many points with irregularly 
related phases. The various small parts of the 
target become important when cross section re- 
ductions of the above amount are contemplated. 
The task of screening or covering such parts on 
a ship, for example, is prohibitively difficult. In 
general, successful camouflage can only be ex- 
pected when the target has a relatively simple 
and regular shape. A serious attempt to camou- 
flage a ship would require a completely altered 
superstructure which would interfere with the 
proper functions of the ship, excepting possibly 
certain small vessels. 


129 


130 


TECHNICAL APPLICATIONS OF HARP 


HARP absorbers so far developed as well as 
all other absorbers based upon destructive in- 
terference are inherently wavelength-sensitive. 
The present broadest band HARP film affords 
significant protection over a band about 25 per 
cent in width and simultaneously over another 
narrower band at one-third the wavelength. 
Consequently, they are useful only when the 
enemy radar which is used against a particular 
target lies within these bands. It is obviously 
necessary to forecast the nature of enemy radar 
at the time and place the camouflaged target 
will be employed. 

An example of camouflage will illustrate these 
factors. In the closing months of World War II 
German U-boats were equipped with Schnorkel 
“breathing tubes” which enabled the U-boat to 
remain submerged for long periods of time. The 
exposed part of the Schnorkel was a relatively 
simple rounded shape which projected less than 
ten feet above the surface. Its detection at night 
was only possible with airborne microwave 
radar. The Schnorkel was covered with absorb- 
ent material which was effective against the 
microwave airborne radar used by the Allies. 
The latter sets had been designed and produced 
only for bands at 9.1 cm and at 3.2 cm so that 
a single absorbing layer was effective against 
both bands. The uncovered Schnorkel was in 
itself sufficiently difficult to detect and the ca- 
mouflage made it impossible to locate with the 
existing equipment. It will be noted that, for 
this target, a reduction in maximum range by 
a factor 2 against airborne search was really 
important, that the target was relatively simple 
in shape, and the limited wavelength range for 
which the camouflage was effective could be 
chosen to cover all types of existing airborne 
microwave radar operated by the Allies. 

The return radiation from a simple target 
can be considered as specularly reflected if the 
target presents a surface normal to the inci- 
dent direction which has a radius of curvature 
greater than a half wavelength. The corre- 
sponding cross section will be designated by 

“The “Wesch” absorber.®^ It consisted of 20% synthetic 
rubber impregnated with 80% carbonyl iron. Its electro- 
magnetic properties were similar to sample 2027, Figure 
2, Section 11.2, measured values of cr and fir being 3 and 
7, respectively. Much higher metal concentration than 
that in HARP was necessary because the iron particles 
were spheroidal rather than flakelike in shape. 


oTs. If the return radiation is due to the second- 
ary maxima in the diffraction pattern of a 
large surface or if the surfaces normal to the 
incident direction have radii of curvature less 
than a half wavelength, it will be considered as 
diffracted radiation. The corresponding cross 
section will be designated by o-^. In complex tar- 
gets, the scattered radiation originates from 
the various scattering points in the target and 
will generally be composed of both diffracted 
and specularly reflected waves. In terms of o-« 
and (Ta the total cross section is given by 

0 - = (Ts + (Td + 2 V CgO-d cos (f) . (I) 

where </> is the phase difference between the re- 
sultant specularly reflected wave and the re- 
sultant diffracted wave. If specular reflection 
is present at all, o-« is usually considerably 
larger than o-d. 

HARP absorbers behave quite differently for 
specularly reflected and for diffracted radia- 
tion. With narrow-band HARP, the specular re- 
flection is much reduced while the diffraction is 
unchanged in magnitude. The removal of the 
principal diffraction maximum (specular reflec- 
tion) and the slight change in the secondary 
maxima (diffraction) were shown in Figure 9, 
Section 11.2. Hence, the application of narrow- 
band HARP to a target will only be effective if 
the cross section is mainly specular. A large 
scale test on a model submarine hull 100 ft 
long made at Fisher’s Island^^ illustrated this 
behavior very clearly. The strength of the return 
echo was measured, with the target at a fixed 
range, as a function of orientation. The un- 
covered target gave a strong maximum, about 
12 to 15 db above the signal for other orienta- 
tions, when the target was beam-on. It was 
clearly due to the large and relatively flat sur- 
faces which were then normal to the incident 
direction. When the surface was covered with a 
HARP absorber whose refractive index was 
about 30, the return signal was approximately 
the same in all orientations. The beam-on maxi- 
mum had been reduced to the level of the scat- 
tering for the other orientations. 

In a second test conducted by the Navy^^*^^ at 
the Patuxent River Naval Air Station the ef- 
fectiveness of HARP in reducing ag was also 
demonstrated. The target was a metallic right 
cylinder, 6 ft high and 6 ft in diameter. 


IDENTIFICATION 


131 


mounted on a raft. As the sides of the cylinder 
were perpendicular to the water, the radiation 
specularly reflected from the cylinder was again 
reflected from the water directly back on the in- 
cident direction. Therefore in smooth water the 
return radiation was specularly reflected and 
the cross section of the cylinder approximately 
the same as though it were viewed on a line 
perpendicular to its axis. The maximum range 
at which this target could be detected by air- 
borne radar on the S and X band was determined 
for different altitudes of flight. The determina- 
tions were repeated when the cylinder was cov- 
ered with the appropriate HARP. The S-band 
film had a refractive index of 30 while that for 
the X band had an index of 17. It was found in 
all cases that the maximum range had been re- 
duced by a factor of two or more. 

While HARP with high refractive index has 
little effect on the diffracted radiation this is not 
the case for broad-band magnetic HARP. The 
secondary maxima in the diffraction pattern 
which are not too far removed from the princi- 
pal maximum may also be reduced (Figures 9, 
10, Section 11.2). Likewise, the principal maxi- 
mum is still removed when the surface has a 
small radius of curvature (see Table 3b, Sec- 
tion 11.2). It is, therefore, possible with this 
material to diminish 0 -^. This possibility has not 
been exploited. 

123 IDENTIFICATION 

Several possibilities of using HARP to iden- 
tify a radar target have been considered. Each 
involves an arrangement on the target which 
causes periodic variations in the strength of the 
radar echo. This audio-frequency modulation 
may be detected by a suitable modification of 
the receiver and the additional information 
thereby obtained may be used as a basis for 
identification. For airplane targets the rotation 
of the propeller periodically alters the target 
cross section enough to modulate the return 
signal. By applying HARP to the propeller 
blades it is possible to produce new subharmonic 
frequencies in the modulation the presence of 
which serve to identify the target. This system 
is commonly called Sambo. For other targets the 
modulation must be introduced by a rotating 


reflector. HARP is used to insure that the modu- 
lation is only present when the radar signal lies 
within a certain band of wavelengths. This 
system is called Harpoon. The presence of modu- 
lation at some wavelengths and absence at others 
is very difficult to simulate without HARP mate- 
rial. In addition the fact that the modulation is 
only present in a band of wavelengths diminishes 
the chance of its discovery by the enemy. 

A receiver for detecting modulation has been 
discussed by Lawson.^^ There are essentially 
two parts, a pulse lengthening circuit (box-car 
generator) which maintains the peak value of 
the signal in the gate from one pulse to the next 
and an audio-frequency spectrum analyzer 
which employs an audio-frequency amplifier to 
drive a set of tuned reeds. Unfortunately sepa- 
rate audio-frequency channels with independent 
automatic gain controls were customarily used 
so that very little of the data has been analyzed 
quantitatively for the actual percentage modu- 
lation of the various frequency components. As 
a fixed modulation frequency is used in Har- 
poon, the amplifier and reeds can be replaced by 
a narrow band-pass amplifier. An ingenious 
type of analyzer for Sambo has been developed 
by Dunnington^o which indicates directly the 
ratio of the percentage modulation of a subhar- 
monic frequency to the percentage modulation 
of the normal fundamental frequency. 

A useful criterion for the degree of modula- 
tion is the ratio of the desired signal intensity 
to the intensity from other causes at the same 
modulation frequency. It is termed the signal- 
to-noise ratio. Analysis shows that noise arising 
from the receiver as well as from neighboring 
pulse transmitters operating on the same wave- 
length may be minimized by using as narrow a 
gate as possible to reduce interference and by 
using a high repetition rate to reduce the effect 
of beats between the high harmonics of the sig- 
nal modulation and the repetition frequency. 
The normal receiver noise is only important for 
very weak signals. The remaining source of 
noise is the target itself since fluctuations in its 
cross section are reproduced in the output of the 
pulse lengthening circuit. For example, if two 
airplanes are in the gate at the same time, the 
noise level becomes high because the phase of 
the signal from one plane changes very rapidly 


]32 


TECHNICAL APPLICATIONS OF HARP 


with respect to that from the other (doppler ef- 
fect) . Also if the orientation of a large target is 
rapidly changed, a higher noise level appears 
for a similar reason. A study of the frequency 
distribution of such noise is necessary in the 
proper design of a Harpoon system for the iden- 
tification of ships. 

The noise level essentially determines the 
time, ty required for the indication of modula- 
tion. The frequency band containing the modu- 
lation signal is approximately 2/t. If the modu- 
lation is sufficiently strong to give a signal 
recognizable above the noise in this band, then 
the indication is possible in the time t. As t is 
increased, an improved signal-to-noise ratio re- 
sults until the band width has been narrowed to 
the inherent frequency stability of the modula- 
tion source. In practice band widths of a few 
cycles have been found necessary. The time t 
is therefore of the order of one second. As scan- 
ning systems are not “on target” this long the 
indication of modulation is generally confined 
to tracking systems. 

A new physical principle, introduced by one 
of the authors,^’ which is unrelated to HARP, is 
the basis for Sambo. This is the generation of 
subharmonic frequencies in the propeller modu- 
lation by removing the symmetry of the propel- 
ler. Normally the blades of a propeller, in general 
n in number, are identical so that the configura- 
tion of the plane and propeller is exactly re- 
peated when the propeller rotates through an 
angle of 360 °/?l Hence if v^, is the frequency of 
the shaft rotation, the lowest frequency appear- 
ing in the modulation is If now the blades 
of the propeller are made electrically dissimilar, 
the frequency vq appears in the modulation, as 
well as its harmonics. This result can be ob- 
tained by coating one of the blades with HARP. 
For the resonant wavelength this blade is no 
longer equivalent to the others. In practice all 
the blades are covered to preserve the mechan- 
ical balance of the propeller, and the dissimi- 
larity achieved by painting one or more of the 
blades with a conducting silver paint. 

The reliability of Sambo in discriminating be- 
tween friend and foe depends upon the absence 
of a subharmonic frequency in an untreated 
plane. A large number of observations have 

‘’0. Halpern. 


been made by various agents with conflicting 
results. Lawson and his collaborators found 
these frequencies, called pseudo-Sambo fre- 
quencies, in many instances. They were but 
rarely seen with the equipment operated by 
Group 45. With a special installation at Brigan- 
tine, New Jersey, designed by MIT-RL for the 
purpose, pseudo-Sambo frequencies were never 
seen although hundreds of F6F targets were 
examined and the propeller modulation ap- 
peared normal in all respects. Likewise in many 
contacts made with the Dunnington receiver, 
pseudo-Sambo modulation never exceeded 5 per 
cent of the normal propeller modulation. It is 
probable that while pseudo-Sambo effects are 
present, they are of negligible importance and 
do not appear unless the system is operated in 
a way to detect very small percentage modula- 
tion. 

The reliability of Sambo in providing positive 
identification depends upon the consistent 
presence of propeller modulation. The greatest 
part of the modulation is probably due to re- 
flections from the fiat or slightly rounded sur- 
faces of the propeller blades. Hence strong 
modulation is usually present for a cone of 
angles about 30° in the forward direction. For 
Sambo the performance can be much improved 
by a spinner over the hub of the propeller. When 
one half of the spinner is covered with HARP 
(actually the whole spinner is covered and one 
half painted with conducting paint), a strong 
Sambo signal is present in a much larger cone, 
80°, around the forward direction. In fact with 
the spinner treated it is no longer necessary to 
cover the propeller blades, thereby avoiding the 
difficult problem of permanently adhering 
HARP to the blades. The spinner provides bet- 
ter modulation because the reflection from it 
does not fluctuate violently for small changes in 
angle as is the case for the reflection from the 
surface of a propeller blade. This stability more 
than compensates for the smaller reflecting sur- 
face of the spinner. It may also be noted that a 
spinner divided into four quadrants, of which 
the opposite pairs are alternately reflecting and 
absorbing will generate a modulation frequency 
2v,„ instead of v,,. Hence if it is used with a 
three-bladed propeller, it provides a positive 
means of distinguishing Sambo from pseudo- 


REFLECTION IN SPECIFIC RADAR INSTALLATIONS 


133 


Sambo as the latter always includes the fre- 
quency vq. 

Work on Sambo has shown that it is a feasible 
system of identification. The fact that no elec- 
tronic equipment is carried on the plane, elimi- 
nating failures from this source, is a great ad- 
vantage. There is no corresponding disadvan- 
tage in that the methods of applying HARP 
have been developed to a point where the service 
life of a propeller treated on its camber face is 
probably as great as that of an untreated 
blade.®^’^® It is surprising and regrettable that 
the positive results obtained with Sambo have 
not led to a far more extensive trial than the 
system has yet received. 

Harpoon at the present writing is undergoing 
a preliminary test for the identification of small 
ships from aircraft. An airborne radar system 
has been modified for this purpose and rotating 
corner reflectors (rottetes) have been con- 
structed by Bell Telephone Laboratories. 
Rottetes using HARP absorbers to produce the 
modulation were not satisfactory because in 
their design it was necessary to use reflections 
at very large angles of incidence. Against hori- 
zontal search, the rolling of the ship therefore 
interfered with their operation. The rottetes at 
present being tested use normal rotating corner 
reflectors which are enclosed in a radome cov- 
ered with transmission HARP. The corner re- 
flector is therefore only effective for the wave- 
length band which is transmitted by the HARP 
filters. To a large extent the success of these 
tests will depend on the skill with which the air- 
borne radar has been modified to detect the 
modulation for it is clear that the major prob- 
lem in an airborne set is that of keeping the 
radar trained on the target. It will be noted that 
this problem would be much simpler for a ship- 
borne set and that this system is therefore much 
easier to develop for ship-to-ship identification. 

In concluding this section, a scheme for iden- 
tifying buoys or similar targets for navigational 
purposes may be mentioned. If such a target is 
covered with directional HARP, its cross section 
could be made small for one polarization of the 
incident wave and large for the other. The tar- 
get, if examined by a radar set whose polariza- 
tion could be varied, would then be distin- 
guished by the relative strength of the return 
echo for various polarizations. 


12 4 REFLECTIONS IN SPECIFIC RADAR 
INSTALLATIONS 

The operation of radar systems is often im- 
paired by reflections from structures near the 
antenna or from parts of the antenna support. 
Such reflections give rise to a variety of effects. 
Echoes resulting from illumination of the tar- 
get by these reflections rather than the main 
beam may produce ^‘ghosts” on the plan position 
indicator [PPI]. Reflections directly back into 
the antenna may disturb the operation of the 
transmitter. Interference between the reflected 
and the direct radiation from the antenna may 
seriously distort the antenna pattern of the 
system. Examples of each of these defects and 
its correction by HARP will be discussed. 

The presence of side lobes in an antenna pat- 
tern is generally harmful for operation in a 
congested area. If, for example, a side lobe in 
the antenna pattern is 20 db down from the 
main beam, there is a 40-db discrimination in 
favor of the radar echo from a target illumi- 
nated by the main beam as compared to the 
echo from the same target illuminated by the 
side lobe. Nevertheless, a large and nearby ob- 
ject often gives a signal from side lobe illumina- 
tion which is well above the noise level of the 
system and registers on the PPI, as a target. 
Since this signal appears when the relative bear- 
ing of the antenna with respect to the target 
is not zero but is equal to the angle between 
the main beam and the side lobe, it is properly 
termed a “ghost” or a “false target.” It can 
readily be imagined that the presence of ghosts 
in an area containing many targets is a source 
of confusion in interpreting a PPI presentation. 

When the main beam of the antenna illumi- 
nates any nearby structure, a portion of its 
energy is deflected into a different direction. 
Consequently, the antenna pattern of this in- 
stallation will have additional side lobes at the 
angles corresponding to the directions in which 
energy has been deflected from the main beam. 
In general the interfering structure must inter- 
cept a considerable fraction of the energy in the 
main beam before side lobes of significant 
strength appear. Side lobes arise in the same 
way when a considerable fraction of the energy 
from the antenna feed illuminates supporting 
members of the reflector. These side lobes are 


134 


TECHNICAL APPLICATIONS OF HARP 


the source of ghosts which differ from ghosts 
from the normal side lobes in the feed and re- 
flector itself only in that they do not appear at 
fixed angles with respect to the main beam but 
rather for certain bearings of the antenna with 
respect to its pedestal. 

In the SG-1 installation aboard destroyers the 
antenna pedestal is located four feet behind the 
mast at a height where the mast is approxi- 
mately 10 in. in diameter. When the antenna is 
pointed toward the bow of the ship, a section of 
the mast approximately 3 ft long is illumi- 
nated by the main beam. Engineers of the 
Raytheon Manufacturing Company made an- 
tenna pattern measurements on a mock-up of 
this installation. They found that for antenna 
bearings such that the mast was illuminated by 
the main beam, very broad side lobes appeared 
which were about 20 db down from the main 
beam. When the illuminated section of the mast 
was covered by a HARP absorber, appropriate 
for the SG wavelength, these side lobes were re- 
duced by at least 10 db. To avoid possible effects 
of curvature in the reflecting surface (cf. Sec- 
tion 11.2), and to insure effective absorption 
over the SG scatter band, relatively broad band 
HARP was used. The antenna in these tests was 
a replacement design in which the side lobes 
had been reduced approximately 30 db. It is evi- 
dent that the mast reflections must be reduced 
to the same level if the benefits of the replace- 
ment design in eliminating ghosts are to be 
realized. 

Difficulties from illumination of the pedestal 
in the SK replacement antenna also made by 
Raytheon Manufacturing Company have been 
reduced by HARP. Only a few experimental 
samples of HARP have been made for a wave- 
length of 1.5 m. In tests made by Raytheon engi- 
neers one such sample placed over the illumi- 
nated part of the pedestal considerably reduced 
the side lobe in question. Work on this problem, 
which was in an early stage, was interrupted by 
the cessation of hostilities. 

A slightly different difficulty was involved in 
the SO-5 antenna. Some of the energy from the 
antenna feed passed underneath the reflector, 
thereby giving side lobe in the antenna pattern 
in the backward direction. A baffle to intercept 
the radiation could only change the direction in 


which this side lobe appeared unless the radia- 
tion was absorbed instead of reflected. Tests made 
by Raytheon engineers resulted in a baffle cov- 
ered with HARP appropriate for the SO-5 
wavelength which reduced the side lobe to a 
point where it was no longer important. All pro- 
duction units of this equipment were supplied 
with this HARP covered baffle. 

Reflections from neighboring structures may 
be the source of interfering signals in ground 
installations. In the GCA or 'Talk down’" air- 
craft approach radar system (AN/MPN-1) , the 
antenna is mounted on top of one end of a truck. 
At the other end a structure about ten feet high 
was a source of reflections for some positions of 
the antenna. A HARP screen for the appro- 
priate wavelength placed in front of the struc- 
ture was tested at MIT-RL by Group 104. 
Ground clutter caused by reflections was com- 
pletely eliminated and the operation of the sys- 
tem markedly improved. 

Reflections directly back into the antenna in 
general react on the transmitter and "pull” the 
magnetron off frequency. In the SCR-720 in- 
stallation in the nose of P-61 aircraft the 
antenna rotates through 360°. Strong reflec- 
tions directly into the antenna are present 
when the antenna is pointing backward at vari- 
ous metallic cylinders that house the radar 
equipment. The pulling was sufficient to upset 
the operation of the AFC circuits in this set. In 
tests made at MIT-RL, by Army personnel, it 
was shown that the difficulty was eliminated by 
placing a HARP covering over the metallic 
parts. 

In some airborne navigation systems which 
employ a wide-angle beam, a smooth antenna 
pattern is necessary for the proper functioning 
of the system. If the pattern has large fluctua- 
tions in intensity, a uniformly bright target 
area appears on the scope crossed by a series of 
alternately bright and dark lines the contrast in 
which is determined by the fluctuations in the 
antenna pattern. In order that fluctuations 
should not seriously impair the mapping quali- 
ties it has been estimated that fluctuations in the 
antenna pattern should not exceed 3 db. It is 
clear that reflections from a surface in the 
neighborhood of an antenna can interfere with 
the direct radiation from the antenna to pro- 


SCREENING AND TEST EQUIPMENT 


135 


duce wide fluctuations of intensity in the re- 
sulting pattern (cf. Figure 7, Chapter 11). 

Pattern measurements made by Group 54 of 
MIT-RL on a mock-up of the AN/APS-33 in- 
stallation for P2 aircraft showed fluctuations 
of 16 to 20 db for different elevation angles. 
They occurred when the antenna was pointed 
toward the rear where a long tapered radome 
had been installed over the bomb bay doors. 
They were caused by interference between the 
direct radiation from the antenna and the radia- 
tion from multiple reflections between the ra- 
dome and the surface of the bomb bay doors. 
Installation of HARP on the surface of the bomb 
bay doors reduced the fluctuations due to reflec- 
tions to about 3 db. Incorporation of HARP in 
the radome installation of an AN/APS-33 on 
P2V aircraft has been recommended by Group 54 
to the Naval Aircraft Factory, Philadelphia. 

It should be expected that diffraction in the 
shadow region from a straight edge of an ob- 
stacle, which is due to the sharp boundary of 
the curve front, will not be effected by absorb- 
ent materials on either surface of the obstacle. 
Laboratory tests show that the presence of 
HARP on a screen does not affect the diffrac- 
tion pattern in the shadow region. Hence, dis- 
tortions in an antenna pattern from this source 
cannot be removed by HARP. 

12 5 SCREENING AND TEST EQUIPMENT 

For some purposes it is desirable to reduce 
the radiation from an antenna in certain direc- 
tions. A metallic screen is seldom usable if the 
screen must be installed close to the antenna 
either because the reflection back into the an- 
tenna disturbs the transmitter or because the 
energy is again reflected by other parts of the 
installation into the original direction. HARP 
screening which avoids both difficulties has been 
successfully used for this purpose to reduce the 
altitude line in airborne radar and to reduce the 
cross coupling between neighboring antennas. 
Screening has similarly been used to prevent 
the escape of energy from the antenna of a 
system while it is being tuned up. Absorbing 
screens are also a necessary item of test equip- 
ment whenever a system must be tuned up in a 
space enclosed by metal. Examples of each of 
these uses will be discussed. 


Nightfighter operations, particularly over 
water, have been much hampered by the pres- 
ence of an altitude line on the radar scope. This 
line extends across the scope for all azimuths at 
a range equal to the altitude of the plane. It is 
caused by downward radiation from the an- 
tenna which gives a large signal despite the 
small amount of energy radiated downwards 
because the reflecting area under the plane 
is very large compared to a target. The first 
radar contact is usually made with a target well 
beyond the altitude line. Hence the target must 
be tracked through the altitude line as the dis- 
tance is closed for attack. Contacts are fre- 
quently lost while the target is in the altitude 
line, especially if the enemy is taking evasive 
action. 

The intensity of the altitude line may be esti- 
mated above smooth water. As the water is then 
a perfect mirror, the intensity of the return 
signal can be found from the image of the 
plane in the water. It is clear that, unlike a 
target echo, the altitude signal decreases with 
the square of the distance from the water. It is 
readily shown that the signal from a target 
whose cross section is a and whose range r is 
equal to the altitude of the plane, becomes equal 
to the altitude signal when 

v = ( 2 ) 

where p is the ratio of intensity in the antenna 
pattern in the downward direction to the in- 
tensity in the main beam. For a cross section 
of 100 sq ft and an altitude of 1 mile p = 1/500 
or the side lobe in the downward direction is 
about 26 db below the main beam. Hence, very 
good screening is necessary to reduce the alti- 
tude line to a harmless intensity for altitudes 
of 1 mile or less. 

The British first recognized the possibility of 
eliminating the altitude line by HARP. In a 
series of tests with the AN/APS-4 installation 
on Firefly aircraft (carrier-based planes), very 
satisfactory results were obtained.^^-^® Subse- 
quently the British placed a lend-lease order for 
6,000 sq yd of X-band HARP to equip all Fire- 
fly aircraft of the fleet. 

A series of tests on the AN/APS-6 installa- 
tion in F6F aircraft was initiated by Lieutenant 


136 


TECHNICAL APPLICATIONS OF HARP 


Commander Orphanides at the Charleston, 
Rhode Island, Naval Air Station. It was found 
that the altitude line could be very much re- 
duced by covering the bottom area of the 
radome with HARP and at the same time the 
operation of the radar was not impaired in any 
respect. Previous attempts to screen by metal 
foil had been unsuccesful. This series of tests 
was conducted on a number of planes by several 
experienced combat pilots. A pattern for cover- 
ing the radome was established which gave 
adequate screening and at the same time left 
traces of the altitude line at the extreme azi- 
muths which are useful in navigation. The 
Navy subsequently placed orders for X-band 
and S-band HARP with du Pont Company. A 
pilot plant at the Newburgh Division of the 
du Pont Company was put into operation 
and a total quantity of approximately 3,000 
sq yd of HARP manufactured. The formulation 
studies and production process studies that 
preceded the actual production were made with 
the guidance of MIT-RL.® 

Tests on the reduction of the altitude line have 
also been made in Army planes. At Boca Raton 
a squadron of B-26’s had been equipped with 
SCR-720 radar for training Army nightfighters. 
The ground clutter near the altitude line 
was so severe that practice interceptions could 
not be made below an altitude of 8,000 ft. The 
bottom position of the radomes for the entire 
squadron were covered with HARP. The radar 
for interception purposes was operational for 
altitudes below 4,000 ft. 

In systems employing separate transmitting 
and receiving antennas the coupling between 
the antennas is often a source of difficulty. The 
Radio Corporation of America [RCA] had an 
FM system of this type under development. It 
was necessary that the coupling be weak and at 
the same time constant. A screen covered with 
appropriate HARP was installed behind the 
antennas and tested by RCA engineers. It re- 
duced the coupling due to the backward radia- 
tion of the parabolas and due to backward re- 
flections from the surface of the radome to a 
point where the system was operational. At the 
same time sufficient isolation was provided that 
the coupling was independent of any changes 

* Under OSRD Contract OEMsr-1199. 


produced by the movement of the operators be- 
hind the screens. 

A similar problem was encountered by Group 
71 of MIT-RL in the design of two beacon an- 
tennas mounted on the same rod. The transmit- 
ter was so closely coupled to the receiver that it 
regularly burned out the crystal of the latter. 
In tests by Group 71 it was found that the sepa- 
ration of the two antennas by a ring of the 
proper diameter covered with appropriate 
HARP reduced the coupling to a point where the 
difficulty was eliminated. These rings were in- 
stalled on all production antennas made at The 
Gilfilan Bros., Incorporated. 

The possibility of screening an antenna with- 
out disturbing the operation of a system led to 
an application of HARP in test equipment. It 
frequently is desirable in tuning up a radar sys- 
tem that no energy be radiated. In some jam- 
ming systems it is essential that there be no 
indication of its presence until the moment the 
jamming begins. Similarly for security reasons 
it is desirable to keep other systems off the air 
while they are being tuned up. Likewise in con- 
gested areas it is necessary to keep systems 
from radiating while these are being tuned up 
to avoid interference with other systems on the 
same wavelength. In all these cases a cap lined 
with appropriate HARP which fits over the 
antenna will prevent the radiation from escap- 
ing and at the same time the absorptive char- 
acter of the material prevents any reaction on 
the system. The absence of reaction is essential 
in order that the system remain in tune when 
the cap is removed. 

The caps made and tested by Group 71 of 
MIT-RL for the BUPX (AN/UPN-3, X-band 
beacon) antenna may be cited as an example. 
The caps were slightly larger than the radome 
over the antenna and were lined with X-band 
HARP. In one test the standing wave ratio in 
the line feeding the antenna was changed from 
1.17 to 1.20 when the antenna was capped. This 
change is far below the tolerance set by tuning 
requirements. Preliminary tests made by the 
Aircraft Instrument Company on a similar cap 
for the Black Maria beacon, AN/APX-14, an- 
tenna indicate that a satisfactory solution to the 
problem will be found. 

The problem of reaction on the radar system 


TERMINATIONS AND LABORATORY USES 


137 


also arises when a set is tuned in an enclosed 
space such as a hangar deck or a shop below 
deck. A folding wedge whose surface is covered 
with HARP has been designed and tested by 
the Naval Research Laboratory. It is placed di- 
rectly in front of the antenna of the system un- 
der test. No measurable reaction is present 
when the antenna is pointed into the wedge. A 
small pickup horn is provided at the center of 
the wedge which may be used to excite an echo 
box or other test equipment. A much larger 
folding screen has been tested by Group 54 of 
MIT-RL for the same use with the Cadillac sys- 
tem (airborne early-warning radar) and was 
found to perform satisfactorily. It may be noted 
for the best results with narrow band HARP, 
the material for these wedges should be slightly 
differently designed than that for use at normal 
incidence inasmuch as the angle of incidence is 
about 45° with the electric vector in the plane 
of incidence (cf. Section 10.2). 

12 ^ TERMINATIONS AND LABORATORY 
USES 

Terminations of HARP material are useful 
in equipment where space is at a premium. 
Their principal practical advantage lies in the 
reduced thickness compared with other types of 
terminations. However, they are suitable only 
for low and medium power levels and for rela- 
tively narrow bands. 

The theory of quarter wave absorbers in a 
closed space has been discussed in the conclud- 
ing portion of Section 11.2. In a coaxial line the 
layer should have the same dielectric constant, 
permeability and thickness as a layer used in 
free space at normal incidence. In a waveguide 
these constants should be the same as that for a 
layer in free space used at an angle of incidence 
0 , equation (69) Chapter 11, and with the elec- 
tric vector polarized perpendicular to the plane 
of incidence. Materials fabricated in large 
sheets can therefore be tested without cutting 
the sheets by arranging the test equipment to 
satisfy these conditions. 

The most difficult step in constructing ter- 
minations is that of cutting the sample to fit the 
waveguide or coaxial line. It has been found that 
the snugness of the fit against the metallic walls 
can cause quite large shifts in the resonant 


wavelength even when the material is attached 
to a metal foil. The latter precaution excludes 
the possibility of an air layer forming between 
HARP and the metallic backing. This effect has 
been insufficiently studied and is probably 
caused by air gaps between the material and the 
metal boundaries which the electric field must 
cross. 

Only a few good coaxial terminations have 
been made. They were about in. thick for 
S band and had voltage standing wave ratios 
less than 1.1 at the resonant point. They were 
cut from broad band magnetic HARP suitable 
for normal incidence. A number of terminations 
were made and used to prevent resonance in the 
plungers of coaxial tuning stubs. As a power re- 
flection coefficient of 10 per cent is entirely ade- 
quate for this purpose, no attempt was made to 
produce terminations with a very low standing 
wave ratio. 

Considerably more effort was devoted to the 
problem of X-band waveguide terminations be- 
cause they were an essential part of a direc- 
tional coupler designed by Group 55 at MIT-RL. 
The thickness of 0.1 in. as compared to II /2 in. 
for other types of terminations was an impor- 
tant advantage in this case. The HARP films 
were adjusted for a 60° angle of incidence with 
the electric vector perpendicular to the plane of 
incidence. The angle given by equation (69) 
Chapter 11, was 45°. The larger angle yielded 
better results, probably because of the exact 
way the terminations, which were cut from a 
large sheet by a punch, fitted in the guide. It 
will be noted that material of substantially 
lower loss than normal incidence material was 
required. 

Several hundred terminations were made and 
tested at 3.2 cm. Table 1 shows the wavelength 
dependence of a typical termination. 


Table 1. The effect of wavelength on a typical 
HARP termination.* 


X in cm 

Power standing 
wave ratio 

3.13 

1.15 

3.20 

1.10 

3.26 

1.07 

3.30 

1.10 

3.35 

1.15 

3.40 

1.22 


♦Sample 1449 in by 1-in. waveguide with an approximate thick- 

ness of 90 mils. 


^RCRKT 1? 


138 


TECHNICAL APPLICATIONS OF HARP 


A summary of the results for a number of ter- 
minations cut from the sample 3510-A-2 is 
given in Table 2. They were tested at 3.2 cm 
in i/2-in- by 1-in. waveguide. 


Table 2. The range of voltage standing wave ra- 
tios for a number of terminations cut from one 
HARP sample. 


No. of 
samples 

Range of power 
standing wave ratio 

18 

1.0 -1.1 

8 

1.1 -1.15 

18 

1.15-1.20 

20 

1.20-1.30 

22 

1.30-1.40 

9 

1.40-1.50 

5 

>1.50 


HARP is often useful in the laboratory when- 
ever high-frequency measurements in which 
there is leakage are undertaken. It may, for ex- 
ample, be used to cut down the leakage coupling 


between high-frequency components in a metal 
container. It may be used as a screen between 
high-frequency components in the same room. 
It is very useful whenever any kind of field 
measurements are made, particularly indoors. 
Disturbing reflections and scattering by parts 
of the room, by the operators or even by the 
probe itself, may be reduced. Likewise if the re- 
flections or scattering from an object are being 
examined, the effect of the supports holding the 
object may be reduced. Whenever such measure- 
ments must be made indoors, a ‘‘dark room” 
lined with HARP makes accurate measure- 
ments possible. In order to secure the best pos- 
sible results for this purpose the walls of the 
room should be cut up into wedges so that there 
are no large flat areas. As the material becomes 
tnore widely available, it should be a very use- 
ful adjunct to research and development in high- 
frequency laboratories. 


GLOSSARY 


AEW. Airborne early warning (Cadillac). AN/APS-20 plus 
other components. A 10-cm radar system to be used 
primarily as cover for naval task forces. Radar information 
from an airplane is relayed to the aircraft carrier. 

.\FC. Automatic frequency control. 

AGC. Automatic gain control. 

AGL. Airborne gunlaying. Any completely automatic airborne 
gunlajing system. 

AGS. Airborne gunsight. A manually operated gun-pointing 
system, in which the operator tracks from a scope indication. 

AI. Aircraft interception. A general designation for systems 
for detecting one aircraft from another. 

AIA. A 3-cm AI system for carrier-based fighter aircraft. 

AIBR. Acceleration integrator bomb release (refers to toss- 
bombing). 

Aided Tracking. A combination of displacement tracking and 
rate tracking, that is, the operator has direct single-knob 
control of both the position and velocity of some reference 
line, such as the sight line or the gun line. 

Amplidyne. a d-c generator in which the response of the out- 
put voltage to changes in field excitation is very rapid; used 
extensively as part of a servo follow-up system. 

AMTI. Airborne moving target indicator. 

.\-X Beam. Radio beacon to guide aircraft. 

AN/. Indicates joint Army-Navy designation for a system. 

AN/APA-. Designates an attachment to an airborne radar 
system. 

AN/APA-5. An auxiliary radar bombsight to be used with a 
search radar such as AN/APS-1, -15, -30, especially for 
low-altitude bombing. 

AN /APA-16. Automatic low-altitude bombing attachment for 
s0s,rch frcIrfs 

AN/APA-40 (40-A). Micro-H Mk II. A delay unit for use 
with AN/APS-15 or AN/APQ-13. 

AN/APA-46. Nosmo. An attachment for bombing radars 
designed to provide synchronous tracking, using the 
Norden sight. 

AN/APA-47. Visar. A system similar to AN/APA-46 (Nosmo) 
in which the visual bombardier performs the radar bombing 
also. 

AN/APG-. Designates airborne radar (“pulsed”) gunlaying or 
gun-sighting systems; also includes rocket-sighting systems. 

AN/APG-1. A 10-cm AI and AGL system. 

AN/APG-2. A 10-cm AI and AGL system. 

AN/APG-3. A 3-cm gunlaying radar. 

AN/APG-4. Sniffer. A 73-cm f-m system for automatic bomb- 
release at altitudes up to 400 ft. 

AN/APG-5. A 12-cm ARC system. 

AN/APG-8. Airborne radar similar to AN/APG-15 for in- 
stallation in B-24. 

AN/APG-13 (13A). Falcon. A 12-cm range-only radar for 
75-mm cannon and rocket fire against water targets and 
isolated land targets. 

AN/APG-13B. Vulture or Overland Falcon. A 10-cm range- 
only conical-scan radar for cannon or rocket fire against 
land targets. 

AN/APG-14. Airborne radar similar to AN/APG-5 for in- 
stallation in B-29. 

AN/APG-15 (15A, 15B). A 12-cm conical-scan AGS system. 

AN/APG-16. A 3-cm gunlaying radar, similar to AN/APG-3. 

AN/APG-19. A 3-cm gunlaying system. 

AN/APG-21. Terry, Pterodactyl, or Automatic Vulture. An 
automatic air-to-ground range-only radar, primarily for 
rocket fire. 

AN/APN-1. A 68-cm f-m radio altimeter, usable up to 4,000 ft. 


AN/APN-19A. Airborne respondor beacon. 

AN/APQ-5. LAB. A low-altitude bombing system. 

AN/APQ-7. Eagle. A 3-cm bombing radar. 

AN/APQ-13. H2X. A 3-cm high-altitude bombing and navi- 
gation radar for use over land, similar to AN/APS-15. 

AN/APQ-16. Airborne radar for precision bombing; consists 
of AN/APQ-7 plus the AN/APA-44 ground-position indi- 
cator. 

AN/APS-. Designates an airborne search or interception radar 
system; frequently adapted for bombing. 

AN/APS-2. ASG. A 9-cm ASV and search radar. 

AN/APS-3. A 3-cm medium and low-altitude bombing radar 
for surface-vessel search and torpedo bombing. 

AN/APS-4. ASH. A 3-cni ASV, AI and search radar for 
carrier-based aircraft. 

AN/APS-6 (6A). A 3-cm search and interception radar, de- 
veloped from AIA. Designed for carrier-based night fighters. 

AN/APS-10. A 3-cm lightweight search and navigation system, 

AN/APS-14. Relay link for transmitting radar information 
from airborne PPI to ground PPI. 

AN/APS-15, 15A. H2X. A 3-cm high-altitude bombing and 
navigation radar for use over land. 

AN /A PS- 16. A 57-cm tail- warning radar.- 

AN/APS-19. A 3-cm search and interception radar. 

AN/APS-20. AEW or Cadillac. See AEW. 

AN/APS-33. 3-cm airborne radar for search and low-altitude 
bombing when used with AN /APA-5. 

AN/APX-14, Airborne identification equipment for use in 
conjunction with X-band radar. 

AN/APX-15. Ella. Identification system (for B-29), depend- 
ing upon propeller modulation. 

AN /ART-22. A 100-cm airborne radar relay transmitter for 
Cadillac. 

AN/ASG-10. A nonradar toss-bombing system. 

AN/CPN-2. Ground beacon for precision navigation. 

AN/CPN-6. An X-band ground respondor beacon. 

AN/CPS-1. See MEW. 

AN/CPS-4. A 10-cm ground medium-range air-transportable 
height-finding radar for use with separate search sets. 

AN/CPS-5. A 23-cm ground early-warning and solid-search 
radar. 

AN/CPS-6. V-Beam. S-band early warning and GCI ground 
radar system. 

AN/MPG-1. A 3-cm mobile radar for fire control of coastal 
batteries against small vessels. 

AN/MPN-1, A 10-cm search and 3-cm precision position- 
finding radar used in conjunction with radio communication 
to direct aircraft into landing approaches. 

AN/PPN-1, 2. VHF responder beacons for paratroops. 

AN/TPN-1. VHF transportable responder beacon. 

AN/TP8-1. A 28-cm medium-range portable radar for general 
search. 

AN/TPS-10. A 3-cm lightweight medium-range early-warning 
radar for air search and height-finding; Radiation Labora- 
tory Little Abner. 

AN/UPN-1, 2, 3, 4. Idtra-portable responder beacons. 

Angle of Attack. The angle (measured in the vertical plane 
through the axis of the fuselage) between the line of flight 
of an airplane and some fixed reference line in the airplane, 
such as the line determined by the leveling lugs, the bore- 
sight datum line or the zero-lift line. It varies with the speed, 
weight, and dive-angle. 

Angle, Drift. The angle, in the horizontal plane, between the 
longitudinal axis of an airplane and its path relative to 
the ground. 




139 


140 


GLOSSARY 


Angle Off. The angle between the line of flight of an airplane 
(usually a bomber) and the line joining it to an aerial target; 
sometimes measured from the nose, and sometimes from 
the tail. 

.\ntenna. a conductor or system of conductors for radiating 
or receiving radio waves. A radar antenna includes the 
transmission-line feed or waveguide feed, the radiating 
elements proper, and the reflector. 

Antenna, Driven. An antenna which receives its power from 
the transmitter through the transmission line. 

Antenna Gain. A measure of the degree to which the radi- 
ation pattern is unidirectional; the ratio of the power per 
unit solid angle in the optimum direction to that from a 
source of equal power radiating isotropically. 

Antenna, Parasitic. An antenna which is not driven, but 
receives its current by induction from one or more other 
antennas. 

Antenna Pattern. The angular distribution of radiated power 
from the antenna assembly. 

Antenna, Yagi. Consists of a reflector behind and a series of 
“directors,” shorter than half a wavelength, which are placed 
in a row in front of a driven antenna. A narrow beam of 
radiation is produced, with the maximum radiation in the 
direction of the line of centers of the antennas (end-fire 
parasitic array). 

AR. Aircraft rocket. 

Arma Resolver. A device used to perform vector addition 
of a-c voltages. 

ARO. An airborne range-only radar system; includes S-band, 
X-band, and f-m systems. 

ASB. A 60-cm Navy radar for surface search by carrier-based 
aircraft. 

ASC. Navy designation for SCR-717B. 

ASD. ASD-1. Early designation for AN/APS-3. 

ASE. VHF airborne radar for surface search. 

ASG. AN/APS-2. 

ASH. AN/APS-4. 

ASJ. Former Navy designation for AN/APS-17, a 12-cm tail- 
warning radar for use in bombers. 

ASV. A radar system for detecting and homing on a surface 
vessel from the air. 

ASVC. A 170-cm ASV system. 

Attenuation. Attenuation of a wave is the decrease in ampli- 
tude with distance along a transmission line, in the direction 
of wave propagation, when the amplitude at any given place 
is constant in time. 

Attenuator. A device for controlling the amplitude of a 
signal. There are two types of r-f attenuators, cutoff 
(operating on the principle of a waveguide below cutoff), 
and dissipative (series resistance, or shunt conductance). 

Autosyn. a synchro device like the selsyn (q.v.). 

• A VC. Automatic volume control. 

Bandwidth. The difference between specified frequencies (in 
cycles per second) of a frequency band; usually these are 
the half-power points in the frequency spectrum. 

Base Line. The horizontal or vertical line formed by the 
movement of the sweep on a cathode-ray tube with deflec- 
tion-modulated presentation, for example, type A. 

BBRL. British Branch Radiation Laboratory. 

Beacon. An interrogated radar transmitter by means of which 
an aircraft can determine azimuth and range with respect 
to the location of the beacon. 

Beamwidth. The angle between the half-power intensities of 
the radiation of an antenna. 

Beavertail. See AN/CPS-4. 

Bias. A potential difference between the electrodes of a 
vacuum tube; usually applied to that between cathode 
and a grid. 


Bias Error. A constant error as opposed to a random error. 

Black Maria. A radar system for the identification of friendly 
aircraft, designed to be used with AEW. 

Blocking Oscillator. An oscillating vacuum-tube circuit 
containing a vacuum tube and a transformer which produces 
pulses at a predetermined recurrence frequency. It may be 
free running or under control of a synchronizing voltage. 

Bomb-Release Circle. For a given airspeed and altitude the 
locus of points at which a bombardier can release his bombs 
and hit the target providing he has the correct heading. 
This term is also applied to the electronic plot of such points 
on a radar scope. 

B Scope. A type of indicator on which the signal appears as a 
bright spot, with azimuth angle as horizontal coordinate 
and range as vertical coordinate. 

B' Scope. Similar to B-scope, with elevation vertical and 
range horizontal. 

BURS. AN/UPN-1, -2. 

BUPX. AN/UPN-3, -4. 

Butterfly. Radar for detection of moving vehicles by an 
aircraft. 

c. Cycles per second. The symbol is also used for this term. 

Cadillac. See AEW. 

Cancellation Unit. A delay unit in which signals returned 
from nonmoving targets are canceled out. 

Cathode-Ray Tube (CRT, Oscilloscope, Scope). A vacuum 
tube in which an electron beam is deflected by means of 
electric or magnetic fields. From the deflection, as observed 
on the face of the tube, the instantaneous values of the 
actuating voltages can be learned. 

Central-Station Computer. An airborne gun-directing sys- 
tem which operates turrets by remote control. 

CH. English long-wave early-warning radar used in a chain 
of stations along the coast. 

CIT. California Institute of Technology. 

Clamp. To hold the base of a waveform or pulse to a given 
potential or current value. 

Clutter. Radar signals from ground, sea, or other reflectors 
appearing in an oscilloscope indication, and interfering with 
observation of the desired target signals. 

COHO. Coherent oscillator. 

Coincidence Circuit. A circuit which transmits a pulse only 
when two or more input pulses coincide in time. 

Conical Scan. A system of scanning in which the axis of 
symmetry of the power beam describes a cone, usually of 
small angle. It is used when the angular position of a target 
must be known accurately. 

Corner Reflector. A metallic or metal-coated structure 
resembling the corner of a cube, particularly effective in 
reflecting a radar beam. 

Cosecant-Squared Beam. A radar beam pattern designed to 
give uniform signal intensity for echoes received by airborne 
radars from distant and nearby objects. The beam intensity 
varies as the square of the cosecant of the elevation angle. 

Countermeasures. Measures to combat enemy radar, such 
as jamming, window, anti-radar paint. Schnorkel. 

Crossover. The line about which the power beam from a 
conical-scan antenna revolves; also the relative power in 
the transmitted beam along that line in the antenna pattern. 

Cross Trail. See Volume 2, Figure 2, Chapter 6. 

C Scope. Presentation in which the signal appears as a bright 
spot with azimuth as horizontal coordinate and elevation 
as vertical coordinate. 

CW. Continuous wave. 

CXAM. 150-cm shipboard aircraft-search radar. 

CXEH. A Navy beacon similar to AN/CPN-6, an X-band 
ground respondor beacon. 

CXBL. Laboratory prototype of SM. 




GLOSSARY 


141 


CXHR. Experimental model of SX. 

db. Decibel, a unit used to express a power ratio. The number 
of decibels equals ten times the logarithm to the base 10 
of the ratio of the two powers: e.g., “3 db down” means a 
50 per cent loss of power. 

Decay Constant. The time required for a quantity to decay 
to 1/e of its original value. See time constant. 

Delay. Refers to a delay in the passage of a current (or 
voltage) from one part of the circuit to another. 

Delay Line. An artificial transmission line which produces 
as output a duplicate of what was given to it a definite 
short time before. 

Detail Part. An element of an assembly, such as condenser, 
resistor, choke. 

Director Sight. In this the gunner controls the line of sight. 
As he tracks, the computer positions the guns; see disturbed- 
reticle sight. 

Dish. Antenna reflector. 

Dipole (Antenna). Two metallic elements, each approxi- 
mately a quarter wavelength long, which radiate the r-f 
energy fed to them by the transmission line. 

Disturbed-Reticle Sight. A computing gunsight in which 
the gunner controls the gun line, and as he tracks the 
computer deflects the sight line from the gun line by the 
amount of the ^computed lead angle. 

“Ditch.” Abandon aircraft. 

Doppler Shift. A shift in the frequency of a wave caused by 
the relative motion of the source and receiver. 

Drift Angle. See angle, drift. 

Driven Antenna. See antenna, driven. 

Drone. A pilotless aircraft. 

Duple xER. An assembly (containing a TR tube) which directs 
the received energy to the receiver and excludes the very 
much greater transmitted energy. This allows the same 
antenna and transmission line to be used for both sending 
and receiving. 

Duty Cycle. Ratio of transmitter time-on to repetition period, 
for example a 1 -m pulse repeated every 500 /xsec would 
have a duty cycle of 1/500. Duty ratio and duty are 
other terms for this. Duty factor is its reciprocal. 

Eagle. AN/APQ-7. 

Echo Bo x. A high Q resonant cavity which receives r-f energy 
through a pickup antenna during the transmitted pulse 
and reradiates this energy through the same antenna im- 
mediately after the pulse. The reradiated energy is picked 
up by the radar set. Since this energy from the echo box 
dies off exponentially, it will appear on an A-scope indicator 
as a flat-topped pulse, resulting from the saturation of the 
receiver by the high energy return, followed by an exponen- 
tial curve. The time from the end of the transmitted pulse 
to the time that the echo box signal is lost in noise is called 
the “ringing time” of the echo box. The echo box may be 
used to test the overall r-f performance of the radar set, 
and if the echo-box pickup is in the antenna beam, the form 
of the antenna pattern can be shown graphically on the 
PPL 

Ella. AN/APX-15. 

E Plane. The plane of the electric vector of a beam of 
radiated power. 

Eureka. Respondor beacon. 

Expanded Gain. The addition of a small portion of the 
indicator sweep voltage to the receiver gain voltage. 

Exponential Smoothing. A function x — x{t) is said to be 
exponentially smoothed when it is replaced by y = y{t) 

defined by the differential equation ^ ^ + y = x) see 

Reference 58 in the Part IV bibliography of Division 14 » 
Volume 2. 


Falcon. AX/APG-13A. 

Firefly. A modification of Butterfly giving a PPI presen- 
tation. 

FM. Frequency modulation. 

Frame Time. Time for a complete scan. 

Frequency Pulling. A change in the frequency of a mag- 
netron or other oscillator caused by a change in the load 
impedance. 

Gain. A power ratio, usually referring to an amplifier. 

Gain, Antenna. See antenna gain. 

Gate. A square voltage pulse which switches a circuit on or 
off electronically. 

GCA. Ground control of approach radar landing system; 
laboratory designation for AX^/MPN-1. 

GCI. Ground controlled interception. 

GEE. A British navigation and bombing technique. 

GEE-H. A beacon-bombing system based on GEE equipment. 

GPL Ground position indicator. 

Ground Range. The distance from a point on the ground 
directly beneath an aircraft to a ground target, or ground 
radar. 

GR-S/Clay 2/1. An organic polymer containing aluminum' 
powder. 

G Scope. A type of indicator presenting a spot with wings, 
which grow as the target approaches; azimuth is the 
horizontal, elevation, the vertical coordinate. 

GTAP. Ground track aiming point. 

Gun Fire Control System, Mark 56. Medium-range radar 
director for control of Navy 5-inch/38 cal. guns against 
aircraft. 

Gun-Roll. A source of error in the computing of a lead by a 
gun sight arising from a neglect of one component of 
rotational motion. 

Gyro Sight. A sight in which the angular rate is measured 
by a gyroscope. 

HARP Material. Antiradar coating which absorbs microwave 
frequency radiation. Material with artificially constructed 
dielectric constant and loss. 

Harpoon. A radar identification system in which a rotating 
corner reflector on a target ship is coated with HARP 
material producing modulation only when the radar signal 
is within a certain band of w^avelengths. 

H-Bombing. Bombing with the use of a navigational system 
in w'hich the aircraft interrogates two ground beacons to 
determine its position. 

Helipot. A helical potentiometer. 

H Plane. The plane of the magnetic vector of a beam of 
energy. 

H2S. S-band bombing and search radars. 

H2X. X-band radars for bombing and search; includes 
AN/APS-15 and AN/APQ-13. 

HF. High frequency; 3,000 to 30,000 kc. 

HVAR. High velocity aircraft rocket. 

I-F. Intermediate frequency. In microw'ave radar, the i-f 
amplifiers are usually centered at 15, 30, or 60 me. 

IFF. Identification as friend or foe. Radar systems which 
usually “interrogate” and receive a coded response if the 
target is friendly. 

Impact Prediction. Computation of bomb-release point. 

In-Out Switch. A switch for causing the range gates to un- 
lock from a target signal and move to lesser or greater range. 

Indicator. A device for displaying a received radar signal; 
usually a cathode-ray tube, although a dial or drum recorder 
may occasionally be meant. 

Interrogator. A transmitting IFF radar set. Signals from 
it are received by a transponder, and the latter replies 


r^CRET"] 


142 


GLOSSARY 


automatically, this reply in turn being received by the 
respondor. 

Intervalometer. a device for releasing a series of bombs at 
predetermined time intervals. 

Jinking. Evasive motion of an aircraft in a series of straight 
line segments connected by curves. 

J Scope. A modification of type A in which the time sweep 
produces a circular range scale near the circumference of 
the CRT face. The signal appears as a radial deflection. 

K Band. Refers to wavelengths around 1 cm. 

Killing Drift. Changing the heading of an airplane to 
compensate for wind, so that its ground track will pass 
through a given target. 

LAB. Low-altitude bombing; AN/APA-5 and AN/APQ-5 
are examples. 

Lead-Computing Sight. A gunsight which computes the angle 
between the bore axis of the guns and the line of sight which 
is necessary to obtain hits. 

LHTR. Lighthouse transmitter-receiver. 

Lighthouse Tube. A small oscillator tube, so called from 
its appearance. 

LO. Local oscillator; a tube which produces a signal with a 
frequency near that of the transmitter. The LO signal is 
mixed with the echo to give a “beat” at intermediate 
frequency which is then amplified and detected. 

Lobe-Switching. Directing an r-f beam rapidly back and 
forth between two or more positions. 

Local Turret. An airplane gun turret controlled by an 
operator located in it. 

Longwave. Refers to wavelengths greater than 1 meter, as 
opposed to microwave radar. 

Loran. a hyperbolic grid system of long range radio naviga- 
tion, in which the navigator observes the difference in 
arrival times of pulses from two known stations. 

L-Scope. a double A-scope presentation, for a double-lobe 
system. Deflections to the two sides of the time sweep indi- 
cate signals from upper and lower (or right and left) lobes. 

MAD. Magnetic airborne detector for submarines under water. 

Magnetron. A transmitter tube which produces the main 
pulse of ultra-high-frequency energy. The flow of electrons is 
controlled by an applied magnetic field instead of a grid. 

Major Assembly. A self-contained combination of sub- 
assemblies and detail parts, such as indicator unit, trans- 
mitter-receiver unit, power unit. 

me. Megacycles per second. One megacycle is a million cycles. 

MC-627. Automatic plotting table for close-support bombing. 

Mark 9, 10, 19, and 35. See radar equipment. 

Mark 56. See gun fire control system, Mark 56. 

MEW. Microwave early warning, a 10-cm ground radar for 
long-range detection or control of aircraft (AN/CPS-1); 
allows continuous plotting, in range and azimuth, of mul- 
tiple targets. 

Micro-H. H-bombing with microwave radar systems. 

Microsecond. 10“^ seconds. 

Microwave Radar. Radar using wavelengths less than one 
meter. 

Mil. Abbreviation for milliradian, an angle of one-thousandth 
of a radian; one degree is 17.45 milliradians. 

Mil, Artillery. An angle equal to 1/6400 of a circle; one 
degree is 17.78 artillery mils. 

Milliradian. See mil. 

MIT. Massachusetts Institute of Technology. 

Modulation. Varying the amplitude of the high-frequency 
signal according to a definite pattern. 

Modulator. Also called a pulser. The jiart of the radar set 
which sends the high-voltage pulse to the transmitter. This 
pulse, in turn, starts the oscillation of the transmitter, 
which emits microwave radiation. 


M-Scope. Modification of type A for range finding. The 
horizontal sweep is displaced vertically as in a step; the 
position of this step can be adjusted by some controlling 
device so that it coincides with the signal, at which point 
the device registers range. 

MTI. Moving target indicator. 

Multivibrator. A form of relaxation oscillator, essentially a 
two-stage amplifier with feedback. It will oscillate of its own 
accord, or through an external synchronizing voltage. 

Mush. A vague descriptive term associated with the phenom- 
enon of angle of attack of an airplane. An airborne fixed gun 
is said to “mush” when its bore axis is elevated above the 
line of flight. 

MV. Multivibrator. 

MX-344. A bombing computer. 

NAB. Navigational Aid to Bombing, early designation for 
II2X radar. 

NDRC. National Defense Research Committee. 

Neoprene. Artificial rubber with carbon black in the ratio of 
2 to 1. 

Noise. A random voltage appearing at the output terminals 
of a receiver with no impressed signal, if the amplifier has 
sufficient gain. On the A-scope noise appears as random 
spikes (“grass”) on the sweep line. It is caused by random 
motions of electrons in the grid circuit of the first amplifier 
tube, to fluctuations in emission, shot noise at the plate, etc. 

Noise Figure. The figure of merit for sensitivity of a receiver. 
Defined as the ratio of the input power to kTB (where k is 
Boltzmann’s constant, T the temperature in degrees Kelvin, 
and B the bandwidth in cycles per second) when the output 
signal power equals the output noise power. Noise figure is 
normally expressed in decibels (db). 

Nosmeagle. Nosmo for h]agle. 

Nosmo. AN/APA-46. 

Oboe. A British bombing technique. 

Offset Bombing. Bombing in which the bombardier (visual 
or radar) sights on an aiming point different from the target. 

OSRD. Office of Scientific Research and Development. 

Own-Speed Sight. Same as vector sight. 

Palmer Scan. A type of antenna scan for searching. 

Parasitic Antenna. See antenna, parasitic. 

Pass-Band. Range of frequencies passed by a filter. 

PB-OSRD. Pacific Branch, OSRD. 

PDI. Pilot’s direction indicator. 

PGP. Pulse glide path experimental aircraft landing system. 

Phantastron. a precision delay circuit. 

Plane of Action. The plane containing the line of motion of 
an aircraft and the target. 

Plumbing. Waveguide and coaxial cable or transmission line, 
with fittings. 

Polyrod. Polystyrene plastic rod. 

Position Firing. A rule-of-thumb procedure for use by an 
aerial gunner whose gun is equipped with a ring and post 
sight. The lead taken depends only upon the relative bear- 
ing of the target. 

PPI. Plan-position indicator. Scope indication with circular 
sweep, showing ground objects in approximately correct 
relationship as on a map. 

Pressurize. The filling of the r-f line with air at a pressure 
greater than atmospheric. Its purpose is twofold: (1) to 
prevent breakdown of the components at high altitudes and 
(2) to protect against transmission losses caused by materials 
in the atmosphere, such as dirt and water. 

PRF. Pulse recurrence frequency. 

Probable Error. A magnitude associated with the measure- 
ment of a quantity such that half of the errors are less and 
half are greater than the given magnitude. 

Proximity Fuse. A fuse for shells, bombs, or rockets which 


GLOSSARY 


143 


sends out radio waves and explodes at a predetermined 
distance from a target (VT fuse). 

Pulse. Refers to the emission of power for a short time, fol- 
lowed by a period of no emission; one of the fundamental 
characteristics of most radar systems. 

Pulsed Doppler Shift or Principle. See Division 14, 
Volume 2, Part V. 

Pulse Shape. The graph of radiated energy as a function of 
time. 

Pursuit Course. A course in which a pursuer is continuously 
moving in the direction of the pursued; see Division 14, 
Volume 2, Section 21.1.1 for more complex modifications of 
this concept, such as lead pursuit, aerodynamic pursuit, and 
aerodynamic lead pursuit course. 

Q (of a resonant system). The Q of a specific resonance mode 
of a system is 27r times the ratio of the energy stored to the 
energy lost per cycle, when the system is excited in this mode. 
A high Q circuit is lightly damped, has a small decrement, a 
sharp resonance peak, and a high selectivity. Q is a figure 
of merit. 

Radar. Abbreviation of “radio detection and ranging”; usually 
refers to systems using ultra-high-frequency waves, with 
the pulse technique. 

Radar Equipment, Mark 9. A 10-cm ship fire-control radar 
for AA batteries ; used with Gun Director Mark 45 ; obsolete. 

Radar Equipment, Mark 10. A 10-cm ship fire-control radar 
for AA batteries; obsolete. 

Radar Equipment, Mark 35. A 3-cm automatic-tracking 
radar, an integral part of the Gun Fire-Control System, 
Mark 56. 

Radiation Laboratory. In this book this designation is re- 
served for the Massachusetts Institute of Technology Radia- 
tion Laboratory which carried on radar research and devel- 
opment from 1940 to 1945 under the direction of Division 
14, NDRC. 

Radome. A general name for radar turrets which enclose 
antenna assemblies. 

Range Mark. One of a series of spots or lines on a scope to 
indicate the range of target signals. 

Range Wind. The component of the wind in the direction of 
the target. 

Rate End. A component of the Norden sight. 

Rate Sight. A gunsight in which the lead is computed from 
the rate of tracking of the target. 

RC Network. A circuit containing resistances and capaci- 
tances. 

RC-294. Plotting board for SCR-584. 

Rebecca-Eureka. See Division 14, Volume 2, Section 10.4.2. 

Receiver Sensitivity. Related to the ability of a receiver to 
detect weak signals. It is measured by the noise figure (q.v.) 
in the case of microwave radar. 

Reflector, Corner. See corner reflector. 

Responsor. See interrogator. 

r-f. Radio frequency. A general term for the frequency to be 
radiated, not confined to any specific limit. 

r-f Head. A major assembly unit of a radar system which in- 
cludes the magnetron, duplexer, part or all of the receiver, 
and occasionally other parts. 

RHI. Range-height indicator. 

Ringing Circuit. A circuit in which the oscillations die out 
slowly, as when a bell is rung. 

Ringing Time. See echo box. 

RL. Radiation Laboratory of the Massachusetts Institute of 
Technology. 

Rottetes. Rotating corner reflectors used in the Harpoon 
identification system. 

Sambo. A radar identification system in which HARP film is 
applied to the propeller blades of the target aircraft produc- 


ing new subharmonic frequencies in the normal propeller 
modulation. 

Sawtooth Sweep. A sweep in which the motion of the electron 
beam is controlled by a sawtooth voltage wave, that is, the 
voltage rises slowly and linearly and then declines rapidly. 

S-Band. Refers to wavelengths of the order of 10 cm. 

Scanner. A device which directs the r-f beam successively over 
all points in a given space. 

SCI. Ship-controlled interception. Similar to GCI. 

Scope. Oscilloscope, cathode-ray tube. For the various types 
of scope presentations, see under the appropriate letters. 

SCR. Signal Corps radio set. 

SCR-520. A 10-cm airborne search and interception radar. 

SCR-540. A 155-cm airborne radar for detection of other 
aircraft. 

SCR-582A. An 11-cm fixed coastal-surveillance radar for use 
against ships and low-flying aircraft. 

SCR-584. IVIobile medium-range search and track radar, de- 
signed for antiaircraft fire control, and also applied to 
ground control of aircraft. 

SCR-598. Prototype of AN/MPG-1, not mobile. 

SCR-615A. 1-cm fixed medium-range radar for search, height- 
finding and GCI. 

SCR-682A. A 1-cm long-range coastal search radar for detec- 
tion of ships and low-flying aircraft. 

SCR-695. A 160- to 191-cm transpondor. 

SCR-702A, B. Former Army designations for AN/APG-2, and 
AN/APG-1, respectively. 

SCR-717. An airborne radar system for detection of surface 
vessels. 

SCR-718. A 68-cm pulsed altimeter for use up to 40,000 feet. 

SCR-720. A 10-cm airborne search and interception radar, 
especially for nightfighters. 

SCR-729. An IFF interrogator-responsor. 

Second Detector. The detector which converts i-f (30 or 60 
me) into video. 

Sector Scan. Motion of the scanner reflector back and forth 
through a limited angle, instead of through 360°. 

Selsyn. A self-synchronous motor or generator (autosyn, 
synchro; the latter name has been chosen by the Services). A 
means of making a shaft rotate by the same amount as 
another shaft at some remote position. 

Servo System. A mechanical, frequently electromechanical, 
system for transmitting accurate mechanical position from 
one point to another by electrical or other means. The 
position is corrected by feeding back an error signal. 

Servo-Amplifier. The amplifier of power impulses in a servo 
system. 

Servo Loop. That collection of elements in a servomechanism 
which measures the error in the quantity to be controlled 
and applies a correction tending to reduce that error to zero. 

SC, SG-1. A 1-cm shipborne long-range surface-search radar 
for use on battleships, cruisers, and destroyers. 

Shoran. Short range navigational system, made up of two 
ground radars (AN/CPN-2) and one airborne set (AN/ 
APN-3). 

Side Lobe. A portion of the beam from a radar antenna other 
than the main lobe; usually much smaller. 

SiNEPOT. Sine potentiometer. 

SK. A 150-cm shipborne long-range aircraft search radar for 
installation on battleships, carriers, and cruisers. 

Skiatron. Dark-trace cathode-ray tube used in projection 
plan-position indicators. Navy type VC. 

Skid (of an airplane). Motion of an airplane in a direction 
different from that in which it is heading. 

Skywave. a radio wave reflected from the ionosphere; this 
occurs at frequencies less than 20 me. 




144 


GLOSSARY 


Slant Range. Range from an aircraft to a ground target or 
radar; distinguished from ground range. 

SM. A 10.7-cm high-povver radar for fightei direction and 
surface search on aircraft carriers. 

Sniffer. AN/APG-4. 

SO-5. 5-cm surface-search radar for installation in PT boats 
and landing craft. 

SP. Lighter, simplified model of the SM radar. 

Spinner. Rotating antenna assembly; a scanner. 

SS Lor AN. Sky wave synchronized Loran. 

Stability (of a sighting system). Stability exists when, if the 
gun is given a small quick jerk in some direction, the 
reticle is jerked in the same direction. 

Stabilize (as a scope, or line of sight). To maintain a system 
in a desired orientation, in spite of motion of aircraft or ship. 

Stadiametric Ranging. Determination of range to an air- 
plane target by bracketing the image between optical 
markers in the sight, which then computes the range b\ the 
principle of similar triangles. 

Storage Tube. See Section 23.3.2b. 

SU. 3-cm medium-weight, medium-power SSV radar for use on 
DE’s and other small vessels. 

Subassembly. A part of a unit assembly, replaceable as a 
whole, consisting of a combination of detail parts (q.v.), 
such as i-f amplifier section or voltage regulator. 

Sweep. The beam of electrons passing from the electron gun 
to the face of the CRT makes a point of light on the face of 
the tube. By proper voltage or magnetic control this point 
of light can be made to move in any direction. By making 
this motion rapid and continuous, the point of light becomes 
a line of light, and is called a sweep. 

Sweep Circuit or Generator. A circuit which produces at 
regular intervals an approximately linear or circular, or 
other form of movement (sweep) of the beam of the cathode- 
ray tube. 

SX. Combined 10-cm high-power general-search radar and 
high-power fighter-direction radar for carriers. 

Synchro. Same as selsyn, autosyn. This designation is pre- 
ferred by the Services. 

S’JNCHRONiZATiON (of a bomb-sight). Establishment of the 
proper rate of motion of the bombing computer index so that 
the index tracks the target. 

Synchronization (of a gunlaying system). Establishment of 
the tracking of a target in range and angle, by the gunlay- 
ing system. 

Terry. AN/APG-21. 

Test Equipment. An assortment of instruments provided 
with a radar set to enable the maintenance man to deter- 
mine accurately whether the set is performing properly in its 
various functions, and to aid in locating improperly operating 
components and in restoring them to proper condition. 

Thermistor Bridge. A bridge with sensitive resistors whose 
resistance varies significantly with temperature. 

Time Base. The sweep on an indicator tube begins at zero 
time, the instant that energy is transmitted, and ends at a 
later predetermined time. It may be called a time base. 
Since time and distance are proportional in the radiation of 


the energy from its source, the distance of any signal on the 
sweep from the beginning of the sweep may be translated 
into units of geographical distance. In some circuits, the 
beginning of the sweep is delayed for a fixed or variable 
time after the firing of the transmitter. It is then known as 
a delayed sweep. 

Time Constant. The time required for a variable which obeys 
an exponential law to change by a fraction 1/e of the total 
change. 

TR. Transmit-receive tube; a TR box or, preferably, switch, 
is the assembly containing the TR. See duplexer. 

Trail. The vector giving the displacement of the actual point 
of impact of a projectile or bomb from the point where it 
would have hit if it had moved in a vacuum. 

Trajectory Drop. The angle (in mils) between the line along 
which a projectile was fired and the line from the gun to the 
position of the projectile. 

Transpondor. a radar system which receives and replies to 
an IFF interrogator (q.v.). Also a similar system used as a 
radar beacon for navigational purposes. 

TRE. Telecommunications Research Establishment (British). 

Trigger Pulse. A pulse which starts a cycle of operations. 

Tuning. The process of adjusting circuits to resonance with 

the frequenej^ of a desired signal. 

UBS. Universal bomb sight. 

UHF. Ultra-high frequency (200 to 3,000 me). 

V Beam. AN/CPS-6. 

Vector (verb). To direct (an airplane) toward a moving 
target (military usage in aircraft interception). 

Vector Sight. A gunsight which gives the lead as a constant 
times the sine of the angle off. The constant depends upon 
the own speed of the aircraft, altitude, and ammunition. 

VHF. Very high frequency (30 to 300 me). 

Video. Electrical form in which a returned radar echo is trans- 
mitted to the indicator to be made visible. 

ViSAR. AN/APA-47. 

Vulture. AN/APG-13B. 

Waveguide. A hollow pipe, usually of rectangular form, used 
as an r-f transmission line. The limits on the dimensions of the 
pipe are determined by the wavelength to be transmitted by 
the pipe, also by the shape of the pipe and the mode of trans- 
mission. There are other types of waveguides, such as solid 
dielectric cables through which it is possible to transmit 
energy. Waveguides may be straight, twisted, curved, 
tapered, or flexible. 

Window, Chaff. Radar countermeasure, consisting of strips 
of metal foil or metal-coated paper, cut to a calculated size, 
dropped from an airplane. A small quantity of the material 
will reflect as much energy as an aircraft. 

X-Band. Refers to wavelengths around 3 cm. 

XMTR. X-band transmitter-receiver component for airborne 
radar. 

XT-1. Radiation Laboratory designation for SCR-.584 develoj)- 
ment equipment. 

Vagi Antenna. See antenna, yagi. 

YQ. 11- and 170-cm shipborne radar beacon equipment for use 
with Cadillac airborne early-warning systems. 


(^ URET V 


BIBLIOGRAPHY 


Numbers such as Div. 14-111-AI3 indicate that the document listed has been microfilmed and that its title appears in 
the microfilm index printed in a separate volume. For access to the index volume and to the microfilm, consult the Army 
or Navy agency listed on the reverse of the half-title page. 


HARP— MATERIAL WITH ARTIFICIALLY CONSTRUCTED 
DIELECTRIC CONSTANT AND PERMEABILITY 


7 Vi eoreti cal Co nsideratio n a 

1. Rejibction of Plane TFares by Magnetic Substances, Otto 
Halpern, Special Report 146, IMIT-RL, Dec. 3, 1941. 

Div. 14-111-M3 

2. Theory of a Black Body Produced by a Combination of a 
Thin Screen and a Perfect Mirror, Otto Halpern, Special 
Report 148, MIT-RL, Dec. 12, 1941. Div. 14-113-Ml 

3. Theory of a Black Body Produced by a Conibinalioyi of a 
Thin Screen and a Perfect Mirror, Otto Halpern, Report 
154, Feb. G, 1942. (Supplement to RL 148). 

Div. 14-113-M2 

4. Surfaces Which Reflect Radio Waves Poorly, Otto Halpern, 

Report 72, MIT-RL, Nov. 4, 1942. Div. 14-132-Ml 

Fabrication of HARP 

5. Survey of Binders {Use A), Special Protective Coatings — 
I, April to Sept. 4, 1944, G. T. Borcherdt, NDRC-14-344, 
ESP-44-344, E. I. du Pont de Nemours and Company, Inc. 

Div. 14-132-M3 

6. Formulation Studies — Composition Vanables, Special Pro- 

tective Coatings II, Feb. 1 to Aug. 10, 1944, M. S. Raasch, 
NDRC-14-345, ESP-44-232, E. I. du Pont de Nemours 
and Company, Inc. Div. 14-132-M3 

7. Formulation Studies — Physical Processing Variables, Special 

Protective Coatings III, Feb. 1 to Aug. 1, 1944, • V. Freed, 

NDRC-14-346, ESP-44-230, E. I. du Pont de Nemours 
and Company, Inc. Div. 14-132-M3 

8. Pigment Evaluation Studies, Special Protective Coatings IV, 

E. D. Bailey, NDRC-14-347, ESP-44-216, E. I. du Pont 
de Nemours and Company, Inc. Div. 14-132-M3 

9. Film Thickness Evaluation, Special Protective Coatings V, 
Feb. 9 to Jxdy 25, 1944, A. A. Johnson, NDRC-14-348, 
ESP-44-228, E. I. du Pont de Nemours and Company, Inc., 

Div. 14-132-M3 

10. Cross-Knifed Film for Practical Work at MIT, Special 

Protective Coatings VI, March 8 to July 1, 1944, W. V. 
Freed, NDRC-14-349, ESP-44-235, E. I. du Pont de Ne- 
mours and Company, Inc. Div. 14-132-M3 

11. Knife-Casting on Semiworks Wheels, Special Protective 

Coatings VII, March 20, 1944, W. V. Freed, NDRC-14- 
350, ESP-44-248, E. I. du Pont de Nemours and Com- 
pany, Inc. Div. 14-132-M3 

12. Large-Scale Coating Trials Investigation of Fabric-Coating 
Equipment, Special Protective Coatings VIII, Dec. 14, 1943, 
to June 6, 1944, Graham, NDRC-14-351, ESP-44-231, 
E. I. du Pont de Nemours and Company, Inc. 

Div. 14-132-M3 

13. Spray Trials at Toledo — Engineering Phases, Quality 
Phases, Special Protective Coalings, IX, April 2 to June 2, 
1944, A. A. Johnson, NDRC-14-352, ESP-44-214, E. I. 
du Pont de Nemours and Company, Inc. Div. 14-132-M3 

14. Development of Cement and Paint-Making Procedures for 
Scheme A, Special Protective Coalings X, April 17 to Sept. 
12, 1944, B. Graham, NDRC-14-353, ESP-44-246, E. I. 
du Pont de Nemours and Comi)any, Inc. Div. 14-132-M3 


15. Development of Machine-Spraying Process for Scheme A, 

Special Protective Coatings XI, April 1 to Sept. 15, 1944, 
H. D. Foster, NDRC-1 4-354, ESP-44-260, E. I. du Pont 
de Nemours and Company, Inc. Div. 14-132-M3 

16. Characterization of Metal Flakes. Determination of Diameter- 
Thickness Ratio, Special Protective Coatings XII, May 24 
to Sept. 7, 1945, C. G. Wortz, NDRC-14-355, ESP-45-327, 
E. I. du Pont de Nemours and Companv, Inc. 

Div. 14-132-M3 

17. Preparation of Film by Calendering, Special Protective Coat- 

ings XIII, June 19 to Dec. 31, 1944, ^ - B. Pings, NDRC- 
14-356, ESP-44-350, E. I. du Pont de Nemours and Com- 
pany, Inc. Div. 14-132-M3 

18. Formulation Studies — Exploratory Work for New Uses, 
Special Protective Coatings XIV, Sept. 1, 1944 lo Jan. 1, 
1945, B. C. Pratt, NDRC-14-469, ESP-45-106, E. I. du 
Pont de Nemours and Company, Inc. Div. 14-132-M3 

19. Semiworks-Scale Preparation of Machine-Sprayed Films, 
Special Protective Coatings XV, Nov. 11, 1944 lo Jan. 20, 
1945, B. Graham, NDRC-14-467, ESP-45-107, E. I. du 
Pont de Nemours and Company, Inc. Div. 14-132-M3 

20. Surface Adjustment of Use B Film, Special Protective Coat- 

ings XVI, Aug. 20, 1944 lo March 29, 1945, G. T. Bor- 
cherdt, NDRC-14-547, ESP-45-230, E. I. du Pont de 
Nemours and Company, Inc. Div. 14-132-M3 

21. Laboratory Study of Adhesive Systems, Special Protective 

Coatings XVII, Dec. 14, 1943 to April 1, 1945, W. A. Hoff- 
man, NDRC-14-470, ESP-45-105, E. I. du Pont de Ne- 
mours and Company, Inc. Div. 14-132-M3 

22. Semiworks-Scale Preparation of Machine-Sprayed Films, 

Special Protective Coatings XV III, Jan. 1 to June 1, 1945, 
J. H. Baldt, NDRC-14-548, ESP-45-195, E. I. du Pont de 
Nemours and Company, Inc. Div. 14-132-M3 

23. Practical Application Trials {Use A), Special Protective 

Coatings XIX, Feb. 1, 1944 lo April 1, 1945, C. W. Theo- 
bald, NDRC-14-549, ESP-45-231, E. I. du Pont de Ne- 
mours and Company, Inc. Div. 14-132-M3 

24. Practical Application Trials {Uses B and C), Special Pro- 

tective Coatings XX, Aug. 25, 1944 lo Aug. 31, 1945, W. A. 
Hoffman, NDRC-14-550, ESP-45-232, E. I. du Pont de 
Nemours and Company, Inc. Div. 14-132-M3 

25. Formulation Developrnent Studies, Special Protective Coat- 

ings XXI, Jan. 1 to Aug. 31, 1945, E. R. Alexander, 
NDRC-14-551, ESP-45-233, E. I. du Pont de Nemours 
and Company, Inc. Div. 14-132-M3 

26. Preparation of Films by Hot Pressing, Special Protective 

Coatings XXII, Jan. 20 to A ug. 31, 1945, G. T. Borcherdt, 
NDRC-14-552, ESP-45-234, E. I. du Pont de Nemours 
and Company, Inc. Div. 14-132-M3 

27. Semiworks-Scale Prep, of Machine-Sprayed Films, Special 

Protective Coatings XXIII, June 1 to Aug. 31, 1945, B. 
Graham, NDRC-14-553, ESP-45-235, E. I. du Pont de 
Nemours and Company, Inc. Div. 14-132-M3 


145 


146 


BIBLIOGRAPHY 


28. Process Developineni Work at Newburgh, Special Protective 

Coatings XXIV, July 23 to Aug. 31, 1945, J. H. Baldt, 
NDRC-14-554, ESP-45-236, E. I. du Pont de Nemours 
and Company, Inc. Div. 14-132-M3 

29. Final Report of All Work under OSRD Contract OEMsr- 
1199, Special Protective Coatings XXV, Dec. 1, 1943 to Sept 
30, 1945, B. C. Pratt, NDRC-14-508, ESP-45-237, E. I. 
du Pont de Nemours and Company, Inc. Div. 14-132-M3 

Electromagnetic Properties of HARP 

30. A Method to Measure High-Frequency Permeability of a 

Ferromagnetic Body, Otto Halpern, Report 155, MIT-RL, 
Feb. 21, 1942. Div. 14-111-M5 

Technical Applications of HARP 

31. Schornsteinfeger, Technical Report 90-45, U. S. Naval 
Technical Mission in Europe, May, 1945. 

32. Radar Camouflage, M. M. Andrew, Otto J. Baltzer, E. H. 

Hudsbeth, and C. E. Mandeville, Report 766, MIT-RL, 
July 16, 1945. Div. 14-262.2-Ml 

33. Report on Tests of Harp Camouflage Materials with AN / 
APS-2E Radar, Project TED No. PTR — 31A30 Tactical 
Test, U. S. Naval Air Station, Patuxent River, Md., 
Sept. 16, 1944. 


34. Final Report on HARP Camouflage Tests, Project TED 
No. PTR-31A30 Tactical Test, U. S. Naval Air Station 
Patuxent River, Md., May 23, 1945. 

35. Detection of Propeller and Sambo Modulation, James L. 

Lawson, OEMsr-262, Report S-10, MIT-RL, May 16, 
1944. Div. 14-324. 1-M2 

36. A New Secondary Modulation Indicator, F. G. Dunnington, 
OEMsr-262, Report 45, MIT-RL, March 25, 1946. 

Div. 14-242. 12-M7 

37. Physical Performance Tests on Preferred Sambo System 
Under Simulated Service Conditions, Special Protective 
Coatings, W. A. Hoffman, and C. W. Theobald, NDRC-14- 
395, E. I. du Pont de Nemours and Company, Inc. 

Div. 14-132-M6 

38. Preliminary Report on Life Test of HARP-Coated Propeller 
— Failure of SB2C and TBM Propeller Coatings, Project 
TED No. PTR-31A73 Tactical Test, U. S. Naval Air 
Station, Patuxent River, Md., March 17, 1945. 

39. Report on Altitude Line Reduction in AN/APS-4 Firefly 
Installations, Report IV/3/31, Naval Fighter Interception 
Unit, British Admiralty, April 1945. 

40. Report on Altitude Line Reduction in AN/APS-4 Firefly 
Installations, Report IV/3/34, Naval Fighter Interception 
Unit, British Admiralty, April 1945. 


OSRD APPOINTEES 

Division 14 


Chief 

Alfred L. Loomis 


Secretaries 

Edward L. Bowles John G. Trump 

John R. Loofbourow 


Technical Aides 

John C. Batchelor 
Edward H. Cutler 
John L. Danforth 
Henry O. Eversole, Jr. 

{Administrative Aide) 


Frank D. Lewis 
John R. Loofbourow 
Nora M. Mohler 
John G. Trump 
Fletcher G. Watson 


Members 


R. R. Beal 
W. R. G. Baker 
Edward L. Bowles 
Ralph Bown 
Lee a. DuBridge 
Melville Eastham 
Ray C. Ellis 
John A. Hutcheson 
Loren F. Jones 


M ERVIN J. Kelly 
Ernest 0. Lawrence 
George Metcalf 
1. 1. Rabi 
C. Guy Suits 
Frederick E. Terman 
Alan T. Waterman 
Warren Weaver 
H. Hugh Willis 


Section 14.1 Radar Model Shop 

{Discontinued April 1944) 


Chief 

Melville Eastham 

Members 

Lee a. DuBridge A. H. Poillon 

Eli C. Hutchinson C. Guy Suits 

Frederick E. Terman 

Section 14.2 Navigation 

{Discontinued April 1944) 


Ralph Bown 


Chief 

Melville Eastham 


Members 


Donald Fink 

J. Curry Street 


\ STTCRL'T^ 


147 


CONTRACT NUMBERS, CONTRACTORS, AND SUBJECT OF CONTRACTS 


Contract 

Nu7fiber 

Narne and Address 
of Contractor 

Subject 

NDCrc-25 

University of California 

Berkeley, California 

Resnatron tub^s 

NDCrc-53 

Massachusetts Institute of Technology 
Cambridge, Massachusetts 

Superseded by OEMsr-262 

NDCrc-73 

Radio Corporation of America Manufacturing 
Company 

Camden, New Jersey 

Microwave components 

NDCrc-74 

Radio Corporation of America Manufacturing 
Company 

Camden, New Jersey 

Pulse transmitter tubes and receivers for Loran 

NDCrc-150 

Radio Corporation of America Victor Division 
Camden, New Jersey 

Long-delay and dark-trace cathode-ray tubes 

NDCrc-174 

Western Electric Company 

Bell Telephone Laboratories 

New York, New York 

3-cm generator 

NDCrc-175 

Western Electric Company 

Bell Telephone Laboratories 

New York, New York 

Magnetrons and oscillators 

NDCrc-192 

Westinghouse Electric & Manufacturing 
Company 

East Pittsburgh, Pennsylvania 

Laboratory pulsers 

NDCrc-203 

Massachusetts Institute of Technology 
Cambridge, Massachusetts 

Superseded by OEMsr-262 

NDCrc-20o 

Western Electric Company 

Bell Telephone Laboratories 

New York, New York 

Development of receivers for long-range navigation 
system 

OEMsr-2 

Western Electric Company 

Bell Telephone Laboratories 

New York, New York 

Pulse timers for Loran 

OEMsr-5 

Massachusetts Institute of Technology 
Cambridge, Massachusetts 

Raytheon magnetron model shop 

OEMsr-7 

General Electric Company 

Schenectady, New York 

Five experimental permanent magnets 

OEMsr-8 

General Electric Company 

Schenectady, New York 

Magnets and receivers, etc. 

OEMsr-9 

General Electric Company 

Schenectady, New York 

One Loran pulse transmitter and four tubes 

OEMsr-10 

General Electric Company 

Schenectady, New York 

(a) Long-delay phosphors, (b) 10-cm magnetrons, 
(c) two (2) gun turrets 

OEMsr-lo 

Sperry Gyroscope Company 

Brooklyn, New York 

Antenna parabolae and gears 

OEMsr-53 

Sperry Gyroscope Company 

Brooklyn, New York 

Pulse receivers for LRN 

OEMsr-61 

Massachusetts Institute of Technology 
Cambridge, Massachusetts 

Superseded by OEMsr-262 

OEMsr-62 

Massachusetts Institute of Technology 
Cambridge, Massachusetts 

Development of Radiation Laboratory and author- 
ity to develop systems and components originat- 
ing in it 

OEMsr-67 

Sperry Gyroscope Company 

Brooklyn, New York 

Klystron oscillators 

OEMsr-73 

Westinghouse Electric & Manufacturing 
Company 

East Pittsburgh, Pennsylvania 

Pulse transmitters 

OEMsr-74 

Westinghouse Electric & Manufacturing 
Company 

East Pittsburgh, Pennsylvania 

Laboratory j)ulsers 

OEMsr-84 

Raytheon Manufacturing Company 

Waltham, Massachusetts 

3-cm magnetrons 


148 


CONTRACT NUMBERS, CONTRACTORS, AND SUBJECT OF CONTRACTS {Continued) 


Conirnct 

Number 

Name and Address 
of Contractor 

Subject 

OEMsr-llS 

Sperry Gyroscope Company 

Brooklyn, New York 

Additional klystron work 

OEMsr-157 

Western Electric Company 

(Bell Telephone Laboratories) 

New York, New York 

3-cm receiving tubes 

OEMsr-164 

Research Construction Company 

Cambridge, Massachusetts 

Radar model shop 

OEMsr-168 

Sperry Gyroscope Company 

Brooklyn, New York 

Crystal mixer receivers 

OEMsr-180 

General Electric Company 

Schenectady, New York 

Permanent gas thyratrons 

OEMsr-191 

Massachusetts Institute of Technology 
Cambridge, Massachusetts 

Laboratory for insulation research. Development 
and wide frequency investigation of dielectrics 

OEMsr-233 

General Electric Company 

Schenectady, New York 

AGL-1 airborne gun-laying radar system 

OEMsr-248 

General Electric Company 

Schenectady, New York 

Long-delay and dark-trace cathode-ray tubes 

OEMsr-252 

RCA Victor Division (RCA Laboratories) 
Camden, New Jersey 

Noise reduction system 

OEMsr-262 

Massachusetts Institute of Technology 
Cambridge, Massachusetts 

Radiation laboratory 

OEMsr-281 

Link Aviation Devices, Inc. 

Binghampton, New York 

Al-10 training gear 

OEMsr-288 

Westinghouse Electric & Manufacturing 
Company 

Bloomfield, New Jersey 

Cold emission power tubes 

OEMsr-335 

Polytechnic Institute of Brooklyn 

Brooklyn, New York 

Develoi)ment of attenuators and RF test equip- 
ment 

OEMsr-344 

Georgia School of Technology 

Atlanta, Georgia 

Highly selective audio-amplifier and narrow-band 
lock-in type amplifier 

OEMsr-358 

Franklin Institute (Bartol Research Foundation) 
Philadelphia, Pennsylvania 

Magnetron cathode studies 

OEMsr-360 

Franklin Institute (Bartol Research Foundation) 
Philadelphia, Pennsylvania 

Electronic switch 

OEMsr-362 

Purdue Research Foundation 

Lafayette, Indiana 

Crystal detectors 

OEMsr-369 

Zenith Radio Corporation 

Chicago, Illinois 

Lightweight range-only unit 

OEMsr-380 

Sylvania Electric Products, Inc. 

(formerly Hygrade Sylvania, Inc.) 
Emporium, Pennsylvania 

A special tunable intermediate frequency amplifier 

OEMsr-382 

Brown University 

Providence, Rhode Island 

Cathode-ray tube project 

OEMsr-386 

Eastman Kodak Company 

Rochester. New York 

Microwave absorbent paint 

OEMsr-387 

University of Pennsylvania, Trustees of the, 
Philadelphia, Pennsylvania 

Radar-ranging system and high-frequency video 
amplifiers 

OEMsr-388 

University of Pennsylvania, Trustees of the, 
Philadelphia, Pennsylvania 

Crystal research 

OEMsr-429 

Cornell University 

Ithaca, New York 

Theoretical aid 

OEMsr-443 

RCA Victor Division 

(License Division Laboratory) 

Camden, New Jersey 

Loran receiver for receiver trainer 

OEMsr-477 

RCA Victor Division 

Harrison, New Jersey 

Tube model shop services for Columbia Radiation 
Laboratory 

OEMsr-485 

Columbia University, Trustees of. 

New York, New York 

Columbia Radiation Laboratory 


149 



CONTRACT NUMBERS, CONTRACTORS, AND SUBJECT OF CONTRACTS {Continued) 


Contract 

Number 

Name and Address 
of Contractor 

Subject 

OEMsr-486 

Harvey Radio Laboratories, Inc. 

Cambridge, Alassachiisetts 

Six transmitting sets for long-range navigation 
project 

OEMsr-507 

Radio Engineering Laboratories, Inc. 

Long Island City, New York 

Thirty-six Loran transmitters 

OEMsr-511 

Harvey- Wells Communications, Inc. 
Southbridge, Massachusetts 

Fifteen Loran receivers 

OEMsr-o40 

General Electric Company 

Schenectady, New York 

Precision aircraft scanners 

OEMsr-543 

General Electric Company 

Schenectady, New York 

Two truck mounted XT-IA anti-aircraft fire- 
control radars 

OEMsr-546 

University of Colorado 

Boulder, Colorado 

Stable noncrystal controlled low frequency 
oscillator 

OEMsr-557 

General Electric Company 

Four AGL-1 equipments 

OEMsr-560 

Kansas State College 
^Manhattan, Kansas 

Time-delay measuring instruments 

OEMsr-582 

General Electric Company 

Fort Wayne, Indiana and Pittsfield, 
Massachusetts 

Transformer model shop 

OEMsr-583 

Sylvania Electric Products 

Emporium, Pennsylvania 

Special signal generators 

OEMsr-589 

Raytheon Manufacturing 

Newton, Massachusetts 

Transformer model shop 

OEMsr-609 

Leland Electric Company 

Dayton, Ohio 

Three-phase aircraft alternator 

OEMsr-619 

American Machine Defense 

Corporation 

Precision antenna mount for use with the CXBL 
set (SM Prototype) 

OEMsr-633 

Fada Radio & Electric Company 

Long Island City, New York 

Loran receivers 

OEMsr-634 

Carnegie Institution of Washington, 
Geophysical Laboratory 

Washington, D, C. 

Cathode-ray tube screens 

OEMsr-642 

Sperry Gyroscope Company 

Garden City, New York 

AGL-2 fire control system 

OEMsr-652 

University of California 

Berkeley, California 

High-vacuum switch 

OEMsr-663 

Gilfillen Bros., Inc. 

Los Angeles, California 

Ground-control-of-approach landing systems 
AN/MPN-1 (XE-1) and construction of two 

OEMsr-684 

RCA Victor Division (RCA) 

Princeton, New Jersey 

Lightweight Racon Development (BUPX) 

OEMsr-689 

Foxboro Company 

Foxboro, Massachusetts 

Trainer for SCR-584, anti-aircraft fire-control 
radar 

OEMsr-691 

RCA Victor Division (RCA Laboratories) 
Camden, New Jersey 

UHF Propagation Studies 

OEMsr-709 

Westinghouse Electric & Manufacturing 
Company 

Bloomfield, New Jersey 

High-pressure spark gap 

OEMsr-723 

General Electric Company 

Schenectady, New York 

Loran receivers 

OEMsr-728 

State College of Washington 

Pullman, Washington 

Microwave propagation studies 

OEMsr-768 

Cornell University 

Ithaca, New York 

Theoretical aid 

OEMsr-770 

' Harvey- Wells Communications, Inc. 

Southbridge, Massachusetts 

Fifty (50) Loran receivers 

OEMsr-777 

Western Electric Company 
(BTL) 

Interference and field strength study 

OEMsr-781 

Rensselaer Polytechnic Institute 

Troy, New York 

Trigger circuits 


150 


CONTRACT NUMBERS, CONTRACTORS, AND SUBJECT OF CONTRACTS {Continued) 


Contract 

Number 

Name and Address 
of Contractor 

Subject 

OEMsr-789 

Radio iVIanufacturing Engineering Laboratories, 
Inc. 

Long Island City, New York 

Five (5) Loran training equipment 

OEMsr-80o 

Harvey Radio Laboratories, Inc. 

Cambridge, IMassachusetts 

Twenty (20) Loran transmitters 

OEMsr-812 

Fairchild Camera & Instrument Corporation 
(formerly Fairchild Aviation Corporation) 
Jamaica, New York 

(a) AGL central-station computer and (b) AGS 
gyro sight and spinner mount 

OEMsr-821 

Franklin Institute (Bartol Research Foundation) 
Philadelphia, Pennsylvania 

Crystal clock for Loran receiver 

OEMsr-832 

Philco Corporation 

Philadelphia, Pennsylvania 

LHTR unit for ARO radar and construction of 
six (6) 

OEMsr-872 

RCA Victor Division (RCA) 

Harrison, New Jersey 

RF tube development 

OEMsr-874 

Fairchild Aviation Corporation 

Jamaica, New York 

Range follow-up for ARO 

OEMsr-890 

Emerson Radio & Phonograph Corporation 

New York, New York 

Trainer for SH radar 

OEMsr-900 

Carnegie Institute of Technology 

Pittsburgh, Pennsylvania 

Dark-trace cathode-ray tubes 

OEMsr-918 

Galvin Manufacturing Corporation 

Chicago, Illinois 

BPP, portable radar beacon (AN/PPN-2) 

OEMsr-960 

Dalmo-Victor, Inc. 

San Francisco, California 

Development of radar scanners 

OEMsr-972 

Galvin Manufacturing Corporation 

Chicago, Illinois 

Airborne range only ARO and airborne 

OEMsr-977 

RCA Victor Division 

(License Division Laboratory) 

Camden, New Jersey 

Loran receiver developments 

OEMsr-988 

Sylvania Electric Products, Inc. 

Emporium, Pennsylvania 

Radar tube for pulsed and CW operation 

OEMsr-999 

Sylvania Electric Products 

Salem, Massachusetts 

Tube model shop 

OEMsr-1022 

Stevens Institute of Technology 

Hoboken, New Jersey 

Development of electric brushes through power 
metallurgy 

OEMsr-102o 

RCA Victor Division 

Camden, New Jersey 

Lightweight tail warning system (AN/APS-13) 

OEMsr-1029 

RCA Victor Division 

(License Division Laboratory) 

Camden, New Jersey 

Lodar direction-finding receivers 

OEMsr-1032 

Kuthe Electric Company 

Newark, New Jersey 

Development of the H-50 hydrogen thyratron 

OEMsr-1043 

RCA Victor Division 

Lancaster, Pennsylvania 

Radar tube model shop 

OEMsr-1044 

Librascope, Incorporated 

Burbank, California 

Radar bombing computers and ballistic computer 
for gun director Mark 56 

OEMsr-1052 

Galvin Manufacturing Corporation 

Chicago, Illinois 

BGS beacons, construction of Forty 

OEMsr-1054 

Douglas Aircraft Company 

Santa Monica, California 

Antenna installation for project Eagle (AN/APQ-7) 

OEMsr-1089 

International Projector Corporation 

New York, New York 

Model of scanning antenna for Eagle (AN/APQ-7) 

OEMsr-1091 

Wilcox & Gibbs Sewing Machine Company 

New York, New York 

Equation solver for SM and SCR-615 trainers 

OEMsr-1112 

Westinghouse Electric & Manufacturing 

Company 

Sharon, Pennsylvania 

Transformer model shop I 

OEMsr-1127 

RCA Victor Division 

(National Broadcasting Company) 

Camden, New Jersey 

Relay radar system 


151 



CONTRACT NUMBERS, CONTRACTORS, AND SUBJECT OF CONTRACTS {Continued) 


Contract 

Numher 

Name and Address 
of Contractor 

Subject 

OEMsr-1139 

E. I. du Pont de Nemours, Inc. 

Wilmington, Delaware 

Research on sintering of boron and laboratory 
preparation of pure germanium 

OEMsr-1140 

Allen B. DuMont Laboratories, Inc. 

Passaic, New Jersey 

P3I indicator units 

OEMsr-1141 

Allen B. DuMont Laboratories, Inc. 

Passaic, New Jersey 

Development of cathode-ray tube screens 

OEMsr-1143 

Emerson Radio & Phonograph Corporation 

New York, New York 

Power supply for lodar receivers 

OEMsr-1146 

Machlett Laboratories, Inc. 

Springfield, Connecticut 

High-power S-band magnetron 

OEMsr-1149 

General Electric Company 

Schenectady, New York 

Gyro-lead computer sight for the AGS radar 

OEMsr-1162 

Massachusetts Institute of Technology 
(Servomechanisms Laboratory) 

Cambridge, Massachusetts 

Servos for gun director Mark 56 

OEMsr-1165 

Westinghouse Electric & Manufacturing 

Company 

Bloomfield, New Jersey 

K-band transmitter tube developments 

OEMsr-1167 

Chrysler Corporation 

Detroit, IVIichigan 

Radar scanning units for SCR-584 and gun director 
Mark 56 

OEMsr-1186 

Sylvania Electric Products, Inc. 

Salem, Massachusetts 

K-band RF head 

OEMsr-1199 

E. I. du Pont de Nemours, Inc. 

Wilmington, Delaware 

HARP protective coatings 

OEMsr-1212 

Western Electric Company 

New York, New York 

Thermistors for RF power measurement 

OEMsr-1218 

Western Electric Company (BTL) 

New York, New York 

Broad-band TR and anti TR 

OEMsr-1220 

Franklin Institute (Bartol Research Foundation) 
Philadelphia, Pennsylvania 

Loran supersonic trainer 

OEMsr-1239 

Westinghouse Electric & Manufacturing 

Company 

Sharon, Pennsylvania 

Transformer model shop II 

OEMsr-1242 

Chicago Telephone & Supply Company 

Elkhart, Indiana 

Special winding machine 

OEMsr-1269 

LTtah Radio Products Company 

Chicago, Illinois 

Design and sample production of pulse transformers 

OEMsi-1283 

Federal Telephone & Radio Corporation 

Newark, New Jersey 

High impedance cable 

OEMsr-1291 

Maguire Industries, Inc. 

(General Electronics Industries Division) 
Greenwich, Connecticut 

Stabilized scanner for the H2K radar and the 
construction of five (5) 

OEMsr-1295 

Sylvania Electric Products, Inc. 

Emporium, Pennsylvania 

Cathode-ray tube screens 

OEMsr-1299 

General Electric Company 

Schenectady, New York 

Gun director Mark 56 

OEMsr-1306 

General Electric Company 

Schenectady, New York 

Broad-band TR and anti TR 

OEMsr-1311 

California Institute of Technology 

Pasadena, California 

Precision measurement of waveguide discontinui- 
ties 

OEMsr-1336 

General Electric Company 

Schenectady, New York 

Stable base unit for radar antenna 

OEMsr-1337 

Sperry Products, Inc. 

Hoboken, New Jersey 

MTB computing radar sight 

OEMsr-1338 

International Business Machines Corporation 
Endicott, New York 

Counter for Mark III Loran indicator 

OEMsr-1352 

Sylvania Electric Products, Inc. 

Salem, Massachasetts 

Transformer model shoj) 


152 




CONTRACT NUMBERS, CONTRACTORS, AND SUBJECT OF CONTRACTS {Continued) 


Contract 

Number 

Name and Address 
of Contractor 

Subject 

OEMsr-1358 

Fairchild Camera & Instrument Corporation 
Jamaica, New York 

Cameras for aerial radar photography 

OExMsr-1360 

University of Michigan 

Ann Arbor, Michigan 

Infrared absorption by water vapor 

OEMsr-1361 

American Type-Founders 

Elizabeth, New Jersey 

Antenna mounts for high-resolution radar 

OEMsr-1377 

General Electric Company 

Schenectady, New York 

K-band crystals 

OEMsr-1394 

General Electric Company 

Schenectady, New York 

Components for two (2) SCI radars (CXHR) 

OEMsr-1408 

Western Electric Company (BTL) 

New York, New York 

Germanium crystal rectifiers for radar 

OEMsr-1409 

Western Electric Company (BTL) 

New York, New York 

High-power enclosed fixed-gaps 

Purchase Order 600,072 

Western Electric Company 

New York, New York 

Procurement of type D-160207 oscillator 

Purchase Order 600,073 

Western Electric Company 

New York, New York 

Procurement of type D-160537 magnetrons 

Order TPS-38541 

General Electric Company 

Schenectady, New A"ork 

Procurement of one square-wave generator and 
two oscilloscopes 




153 


SERVICE PROJECT NUMBERS 


The projects listed below were transmitted to the Executive Secretary, 
NDRC, from the War or Navy Department through either the War 
Department Liaison Officer for NDRC or the Office of Research and 
Inventions (formerly the Coordinator of Research and Development), 
Navy Department. 


Service 


Project 


Number 

Subject 


Army-Navy Projects 

AN-2 Naloc committee project, in which several NDRC Divisions were concerned. Division 14 was concerned with 
Cachalot. 

AN-3 Corner reflectors for life rafts to increase their range of detection by airborne microwave equipment. Extended to 
consultant to Navy on preproduction engineering of reflectors MX-137/A, MX-138/A, and MX-180/A and to 
their procurement. 

AN-7 Low-altitude bombing attachment for AN/APS-1, AN/APQ-5A. Consultant. 

AN-11 Mark V IFF, Part concerned vith antenna mount accepted. 

AN-18 Development of low frequency Loran with consultant service to the Army. Extension to establishment of a 3-station 
chain, testing and procurement accepted. Extension to participation of Coast Guard in tests accepted. 

AN-19 Assistance to NBS on radio-frequency standards. 

AN-21 Consultant service on K-band AN/APS-30 series and AN/APQ-34. Extended to radomes for AN/APS-32, 34. 
See AC-232.10. 

AN-24 Development of ground position indicators to be used with the AN /APQ-34 and other equipments. 

AN -25 K-band components and techniques. 

AN-27 Airborne identification for propeller modulation. 

Navy Projects 

NA-104 Lightweight X-band search equipment for aircraft. 

NA-109 Stabilizing, control equipment, and target seeking device for radio controlled aircraft; BASN. Divisions 5, 14, 15. 
NA-112 Relay radar, AN/APS-14. 

NA-113 Radar and timing equipment for LAB, AN/APQ-5, low-altitude blind bombing, using ASV now in production. 
NA-117 Development of radar trainers in connection with celestial navigation trainers and observational trainers. 

NA-125 Improved AI equipment with AJ features (AIA-1). 

NA-127 Stabilization of airborne radar antenna systems. Continuation accepted for test of AN/APA-15, K-band spinner, 
AN/APS-1 design improvement. 

NA-128 Development of SM trainers. 

NA-129 Trainer for the type ASH radar, advisory service. 

NA-130 Lightweight radar for controlling searchlights in airplanes. 

NA-131 Aircraft identification system. 

NA-132 Automatic frequency control with application to airborne systems. 

NA-135 Low-altitude bombing trainers for type ASG-1 radar. 

NA-141 Trainer for GCA. Extended to ground-clutter simulator. 

NA-142 Loran bench trainer to use with a Link celestial navigation trainer. Extended to construction of 5. 

NA-160 Trainers for radar equipments AN/APQ-13 and AN/APS-15 (H2X); supersonic trainers. 

NA-163 Racons to be used with X-band radar equipment. 

NA-165 Universal A-J trainer. 

NA-166 Use of terrain models in radar planning; Rapid. 

NA-173 X-band Vixen. 

NA-178 Cadillac, AEW or airborne early warning system. Extended to; Procurement of 40 airborne systems; procurement of 
Black Maria; consultant on GE production; Block III relay radar with construction of 40; ship-centering PPI, 


154 


r CRE 


SERVICE PROJECT NUMBERS {Continued) 


Service 

Project 

Number Subject 


NA-181 

NA-182 


NA-184 


NA-186 

NA-192 

NA-196 

NA-201 

NA-202 

NA-205 

NA-207 

NA-209 


NA-210 

NA-222 

NA.227 

NA-228 

NA-229 

NO-95 

NO-101 

NO-102 

NO-115 

NO-155 

NO-156 

NO-166 


NO-172 

NO-182 


NO-184 

NO-214 

NO-225 


NO-277 

NO-295 

NP-3 

NP-4 

NR-103 

NS-lOO 

NS-101 

NS-107 

NS-108 

NS-114 

NS-118 


N^avij Projects {Continued) 

design and construction of 42; Cadillac 2; 11 CIC’s for B-17’s; Cadillac 3; assistance to Navj on large antenna 
and CIC indicators; extension to Block V relay radar accepted as adviser only. 

Consultant to BuAer and BuShips on development of K-band test set by Aircraft Radio Corporation. 

Application of AN/APG-5 radar equipment to lead computing sights Marks 18 and 21. Consultant on tying-in 
ARO ^^'ith Mark 18 and camera tests. 

Development of test equipment for field maintenance of airborne radio and radar systems, with consultant services. 

Superseded NS-283 and NS-284. Extended to X-band kits of cables and adaptors. 

Fifteen AN/APG-13 radar operator trainers. 

GPI for APS-1. Cancelled on acceptance of AN-24. 

Study of interference fields caused by airborne radar equipment and its components. 

Mechanism for torpedo attack trainer. 

High power intercept radar, HPX. 

Modification of AN/APG-13A to Overland Falcon for Navy aircraft. 

Development of AEW trainer. 

Stub antennas for use on high speed aircraft. Referred to Divisions 13, 14, 15. Assigned to Division 15. Coordination 
with 13 and 14 approved. 

Consultant on detection of Schnorkel by airborne radar. 

Application of HARP material to test equipment. 

Fifty short-time-constant kits for AN/APS-2A, 2D for use against Schnorkel. 

Investigation of X- and S-band antenna patterns for guided missile applications. 

Multiple indicators for AN/APS-30-T1. Accepted as adviser service only. 

Combined radar with Sperry-Draper sight; RO for Mark 51. 

(a) Radar range finder for Ford aircraft fire control. Project taken over by Army Air Corps; (b) radar fire control 
for 0.50 cal. one-man turret. Plans changed from PB2Y3 to B-24 tail turret. 

Radar fire control for flights of 3 seconds, of single seat fighters. Combined with NO-101. 

Radar homing bomb — Pelican. Directive assigned to Division 5 with RL consultant for radar equipment, RHB. 
Blind firing radar for the Mark 52 director; advisor. 

Lightweight antenna for Mark 8 fire-control radar. 

Intermediate range radar and gun director, Mark 56. 

Cooperative Project with Division 7 

Maneuvering-board techniques for radar-directed torpedo attacks. Extended to advisor on procurement and 
installation of Torpedo Director Mark 33. 

Dynamic accuracy of synchro systems. Transferred from Division 6 to Div. 14, RL, Group 56. The section dealing 
with effect of capacity mismatch was accepted. ■ 

IFF transponders for interrogation of fire-control equipment. 

Ballistic range converter, AN/APA-30, ASD-1 attachment; Mk 14 sight. Extended to procurement. 
Shore-bombardment beacons. Extended to design and model-shop production of Mark 2, Mods. 0 and 1 beacons. 
Extended to consultant service. 

Development of trainer for R. E. Mark 8, Mod. 3 and Mark 13, Mod. 0. 

RL, Construction of 6 Auto-Vulture, integrated with Bomb Director Mk3 and Pilot’s Universal Sighting Systems. 
Course in OBJ radar training material. 

Training of personnel in installation and maintenance of SX-radar. 

Detection and ranging system analogous to radar, using pulsed infra-red radiation. Advisor service to Division 16 
accepted by Division 14. 

Recognition system. 

Radar for aircraft carriers to determine the altitude of approaching bombers, CXBL, SM. 

Microwave detection equipment for destroyers; led to SG. 

Microwave detection equipment for submarine chasers; SF, SU; collaboration with Submarine Signal Company. 
Microwave radar for motor torpedo boats. 

Small, lightweight radar equipment for surface-search by motor torpedo boats; SO. Consultant. Extended to beam 
fanning antenna for SO-12. Advisor service only for SO-12M requested. 


\SEf:RE'Tn } 


155 


SERVICE PROJECT NUMBERS {Continued) 


Service 


Project 


Number 

Subject 


NS-119 

NS-120 

NS-126 

NS-127 

NS-131 

NS-133 

NS-135 

NS-138 

NS-148 

NS-149 

NS-153 

NS-156 

NS-162 

NS-167 

NS-169 

NS-171 

NS-174 

NS-175 

NS-176 

NS-177 

NS-178 

NS-184 

NS-185 

NS-186 

NS-188 

NS-190 

NS-192 

NS-194 

NS-196 

NS-223 

NS-224 

NS-227 

NS-228 

NS-229 

NS-232 

NS-234 

NS-237 

NS-246 

NS-249 

NS-250 

NS-265 

NS-268 

NS-270 

NS-271 

NS-272 

NS-273 

NS-274 


Navy Projects {Continued) 

Airborne combined Mark III-G transponder and Mark III interrogator responser; similar to SC-30; collaboration 
with Hazeltine. 

Tracer for superimposing PPI pattern for SG and SF; VPR, 

Ground- and airborne-radar beacons for use with X- and S-band search radar equipments; BGS, BGX. See NS-162. 
Antenna-stabilizing and director-correction unit (RASD). 

Remote-plan indicator (dark trace tubes). 

Consultant to the Navy on the manufacture of equipment for stabilization of shipborne-radar search-equipment. 
Preparation of material suitable for publication in the radar technical bulletins of the Navy Department. 

ASJ tail- warning radar system for aircraft; advisor. 

Broad banding techniques. , 

Precision remote PPI; advisor on VF and VF-1. 

Remote PPI for SR radar. Consultant or advisor on projects of this type. 

Consulting services on SP fighter-director radar; a smaller model of SM. 

Consulting service to the Navy on Philco contract (later given to Galvin) for radar model X-YM (BGX) racon 
equipment. Extended to training for production testing and to theory of operation. 

Camera suitable for taking pictures of a remote PPI screen, SF, SG. 

SSV trainers for use with SF and SG search radar. Extended to consultant on electronic parts and advisor on me- 
chanical target control for trainers for SA, SC, SK and SR series. 

Consultant to the Navy on AI, AN/APS-6. 

Consulting services to the Navy in the production of projection plan position indicators. 

Consulting service on model SG-3 and SU radar equipments. Advisor status only requested. 

Study of SCI methods, including improvements in antenna systems. See NS-194. 

Improvement of shock, vibration and blast resistance of radar equipment. 

Transponder beacon with additional frequencies for use with AN/APS-1. 

Suitable antenna for overhead search and warning. Advisor status only requested. 

Temperature compensated insulation material for use with rotary joints. 

Adaptation of Mark III interrogator-responsers and model ABK series IFF transponder equipments. 

Coded corner reflectors. 

Consultant to Navy on the production of beacon synchroscopes. 

Radar transponder beacons — automatic switching equipment. 

SCI shipborne radar to succeed SM and SP; SX. Extended to vertically scanning antenna for SP-2. 

Test equipment for transponder beacons, including consultant service on TS-120/UP. 

Advisor on interchangeable S-band units for AN/CPN-6 (BGX). Reconsideration of action on consultant service 
accepted. 

Advisor on repackaging SCR-598 for Marine Corps. 

Consulting service for AN/APS-2 (ASG series). 

Consultant for AN/APS-3 (ASD-1). 

Consultant to the Navy for production of AN/APS-15 (H2X). 

Consultant on OBJ trainer (NS-169). Extended to supply of components of OBJ trainer. 

K-band search set for installation on PT boats; CXJG or Cindy. 

Incorporation of antijamming features in SG radar. Advisor status only requested. 

Radar test equipment (especially w^ave selectors and thermocouple dipoles). 

Standards for microw^ave frequencies. 

High resolution X-band radar for small craft. Project Henry. 

Type and production testing of S-band radar echo-box. 

Consultant on solid dielectrics for r.f. cables. Extension to high temperature, high frequency insulation. 
Preparation of final form instruction books for Model C Loran timers. 

Preparation of final form instruction books for Model C-1 Loran timers. 

Improved circuits for Loran transmitter monitor oscilloscopes. 

Antenna coupling units for vertical Loran transmitting masts. Imbedded in NS-275. 

Elimination of screened booths at Loran transmitting stations. 


156 



SERVICE PROJECT NUMBERS (Continued) 


Service 


Project 


Number 

Subject 


NS-275 

NS-276 

NS-283 

NS-284 

NS-285 

NS-286 

NS-29G 

NS-299 

NS-300 

NS-314 

NS-319 

NS-320 

XS-323 

NS-331 

NS-335 

XS-343 

XS-351 

XS-352 

XS-353 

XS-358 

XS-359 

XS-360 

XS-362 

XS-363 

XS-369 

XS-374 

XS-375 

XS-376 

XS-378 


AC-1 


AC-35 

AC-42 

AC-44 

AC-51 

AC-57 

AC-58 

AC-68 

AC-72 

AC-81 

AC-90 

AC-97 

AC-106 

AC-107 

AC-111 

AC-112 

AC-118 

AC-120 


Navy Projects (Continued) 

Study of Loran transmitting antennas. 

Loran test transmitter. 

Consultant on TS-12/AP, airborne X-band test set. Superseded by XA-184. 

Consultant on TS-13/AP, pulsed airborne X-band test set. Superseded by XA-184. 

Consultant on LAD pulsed S-band signal generator. 

Field engineers’ test kit for S-band radar, including consultant on procurement. 

Submarine radar camouflage. Study of nonreflecting surfaces with consultation on other methods. 

Consultant on type A-121 magnetron tube. 

Plastic materials for absorption of electrical radiations. Extended to high loss insulation for wires. 

Consultant to Xavy for AX/APS-1 at Philco. 

Consultant to Xavy for TS-147/UP and TS-147/UP (XX”). 

Consultant on AX/ART-18 and AX/ARR-17 relay links. 

Development and consultant on K-band spectrum analyzer. Extended to conversion of 10 TS-148/UP to K-band. 
Consultant on S-band and Sg-band hand-tuned echo box. Extension to Sw-band accepted. 

Crystal rectifier test set TMX-10 RL. 

Extension of Division 17 project to use of VG-type repeater with dead reckoning analyzer. 

Consultant to the Bureau of Ships for Farnsworth Television and Radio Corp. on AN/APA-5. 

Develoi)ment and consultant services on S-band radar test equipment broad-banding TS-125/UP. 

Development of broad-band TR and ATR system for beacon use. 

Consulting services on coherent pulse modification. 

Development of new SO-type indicator. 

Application of IFF Mark V/UXB to AEW radar. 

Application of IFF Mark V/UXB to SX radar. 

MTI for shipboard radars, especially SP, SR. 

Modification of SCR-584 radars for MTI. 

Reduction of altitude signals in airborne radar. 

Assistance to US Xavy Radio and Sound Laboratory on development of shipboard antenna systems. 

Mk V IFF feed for AX/CPS-6 antenna. 

Panoramic radar. Advisor service only accepted. 

Army Projects 

Precision bombing. Eagle. Procurement of antenna housings. Consultant for problems on antenna within leading 
edge of wing. Replaced by AC-232.01. 

AI-3 system for installatipn in the XA-26B type airplane. 

Radar system and equipment for controlling target-seeking bombs. RHB. Transferred to Division 5. 

Radar-marker float. See AX-3. Replaced by AC-263.08. 

Radar system (SRB) and auxiliary equipment for controlling target-seeking bombs. Transferred to Division 5. 
Plan for the South Atlantic Loran system. 

SS Loran system. 

Test of TG Loran. 

Camera accessories for recording blind-bombing radar display. 

Automatic range finder. See AC-235.01. 

Dielectric properties of synthetic resin glues. Replaced by AC-232.06. 

Detection of armored vehicles by means of radar. Replaced by AC-234.02. 

Procurement of 25 long range plotting boards and kits for SCR-584. Replaced by AC-233.01. 

Investigation of radar requirements on 3-phase 208/120 volt Wye, 400 cycle AC aircraft power supply. 

Xosmo: tie-in of Xorden bombsight and pulse Doppler with H2X. Replaced by AC-232.08. 

Three-tone PPL Replaced by AC-234.03. 

Procurement of X-band Black Maria, XCB. 

Identification of propeller modulation; Ella. Replaced by AC-233.02. 


157 


SERVICE PROJECT NUMBERS {Continued) 


Service 


Project 


Number 

Subject 


AC-220.03 

AC-228.05 

AC-232 

AC-232.01 

AC-232.02 

AC-232.05 

AC-232.06 

AC-232.08 

AC-232.09 

AC-232.10 

AC-233 

AC-233.01 

AC-233.02 

AC-233.03 

AC-233.04 

AC-233.05 

AC-234 

AC-234.01 

AC-234.02 

AC-234.03 

AC-234.04 

AC-234.05 

AC-235 

AC-235.01 

AC-235.02 

AC-235.03 

AC-235.04 

AC-236 

AC-236.01 

AC-236.02 

AC-236.04 

AC-236.05 

AC-236.06 

AC-237 

AC-237.01 

AC-237.04 

AC-237.06 

AC-238.01 

AC-238.06 

AC-239.01 

AC-239.03 

AC-239.04 

AC-239.05 

AC-262 

AC-262.01 

AC-262.09 


Army Projects {Continued) 

Remote control of rockets and pilotless aircraft. Advisor on AN/APW-l; development of AN/APW-3. 
Modification of 245 AN/APlSl-7 to AN/APN-21, for use m remote control of missiles. 

Radar bombing equipment. See the following subprojects. 

Precision bombing, AN/APQ-7. Formerly AC-1. 

Use of airborne radar over land. Extension to consultant to ATSC on development of AN /APQ-13 and AN /APQ-34 
antennas by Boeing Aircraft Corp. Formerly SC-36. 

Cameras. See AC-72. 

Synthetic resin glues. Formerly AC-90. 

Nosmo. Formerly AC-111. Extension to consultant on production of AN/APA-46, 47 by Gibbs, requested. Extended 
to 1,500 manuals. 

Micro-H delay unit AN/APA-40A. 

Advisory service on precision bombing equipment, AN /APQ-34. Replaces Army part of AN-21. 

Radar recognition equipment. See the following subprojects. 

IFF for AGL, AGS and AI. Supersedes SC-119 and part of SC-77. Part referring to SC-119 accepted. 

AN/APX-15 radar modulation detection: test equipment (TS-348 A/AP, TS-364/APX-15), manuals. Extended 
to report on use of corner reflectors for aircraft identification. (Formerly AC-120.) 

Long-range plotting boards and modification kits for SCR-584; procurement of five. Formerly AC-106, SC-101.01. 
True speed of aircraft. Formerly SC-116. 

X-band Black Maria, XCB. Formerly AC-118. 

Radar warning equipment. See the following subprojects. 

Lightw'eight ASV. Extended to development of 30-inch cut-off low-altitude scanner for AN /APS-10. Formerly SC-46. 
Detection of armored vehicles by radar. Formerly AC-97. 

Three-tone PPI. Formerly AC-112. 

Microwave early warning radar, AN /CPS-1. Formerly SC-60 and its extensions. Extended to production of 6 Mark I 
MTI kits. 

Consultant on AEW. 

Radar fire-control equipment and systems. See following subprojects. 

Automatic and aided range finders: AN/APG-5, 13, 14, 21. Extended to modification kits to convert AN/APG-13A 
to B. Formerly AC-81, SC-69. 

AN/APG-15. Formerly SC-69. 

Toss bombing. Formerly SC-80. 

Advisor of AN/APG-3, 16. Formerly SC- 103. 

Radar navigation equipment. See the following subprojects. 

Loran, long range navigation. Formerly SC-56. 

Consultant to ATSC on air transportable Loran, AN/CPN-11, 12. Formerly SC-109. 

Ground controlled landing system, GCA. Formerly SC-53. 

Air transportable GCA, AN/CPN-4. Formerly SC-72. 

Advisory service on automatic radar beacon ranging system with AN/APN-34 and AN/GPN-4. . 

Radar test equipment. Supersedes SC-106. See the following subprojects. 

Consultant on TS-125/AP power meter. Formerly SC-106.01. 

Consultant on directional coupler APA-13. Formerly SC-106.04. 

K-band test equipment. 

Dielectric consultation and tests. 

Reduction of interference. See NA-196. 

SCR-615; height finder for GCI. Formerly SC-71. 

AN/CPS-4; Beavertail height-finder. Formerly SC-75. 

AN/TPS-10; light mountain radar. Formerly SC-107. 

AN/CPS-6; V-beam or “Merry-go-round.” Formerly SC-74. 

Training equipment and systems. Formerly SC-62. 

Trainer AN/APQ-5-Tl(XA). Formerly SC-62.01. 

Crew trainer for H2X. Formerly SC-62.09. 


158 



SERVICE PROJECT NUMBERS {Cojitinued) 


Service 

Project 

Number Subject 


Army Projects {Continued) 


AC-262.10 Trainer for AN/APQ-7. Formerly SC-62.10. 

AC-262.11 Radar trainer for AN/APG-15-T1. Formerly SC-62.11. 

AC-262.12 Procurement of trainers AN/APQ-13-T1. Formerly SC-62.12. 

AC-262.14 Supersonic trainer, AN/APQ-Tl, for precision bombing radars. 

AC-263 Radar beacons. See following subprojects. 

AC-263.02 AN/CPN-8, BPS. Formerly SC-63.02. 

AC-263.03 AX/CPN-6, BGX. Formerly SC-63.03. 

AC-263.04 AN/UPN-1, 2; BUPS. Formerly SC-63.04. 

AC-263.05 AN/UPN-3, 4; AN/APN-11; BUPX. Formerly SC-63.05. 

AC-263.06 K-band beacons. Formerly SC-63.06. 

AC-263.07 Development of S-band beacon, AN/APN-19; Rosebud. 

AC-263.08 Radar marker float. Formerly AC-44. 

AC-301 General directive for MTI. See the following for specific request. Acceptance recommended July 30, 1945. 
AC-301.01 Consultant on development of MTI Mk II for AN/CPS-1. 

OD-47 Radio range-finder for aircraft. 

OD-54 Information for the preparation of bombing tables. 

OD-94 Combined director and radar position-finder for automatic w^eapons. Project handled by a committee of Sections 
D-1, D-2. 


OD-175 Photographic recorder. 

OD-178 Development of field chronograph T-5. 

SC-6 Use of microw’aves for detection purposes. General Radiation Laboratory directive. AI and ASV completed. 

SC-6 was broken dowm into a decimal system and later other numbers were assigned. See SC-51 through SC-62. 

SC-6.12 Development of pulsed glide path, X-band aircraft landing system. 

SC-30 Development of Mark 3-G transponder and Mark 4 interrogator-responder. 

SC-32 Power supply requirements as a function of future radar circuit development. 

SC-33 Weight of radar systems vs. power supply frequency. 

SC-34 Survey of commutation of direct-current machinery at high altitudes. See AC-238.03. 

SC-35 Use of ground radar against ground units. Now' under SC-73. 

SC-36 Use of airborne radar over land (NAB, H2X). Extension to Micro-H, Mark II. See AC-232.62. 

SC-37 Development of radar equipment for use against motor torpedo boats. Consultant service on SCR-598, AN /FPG-1. 

Consultant service on AN /FPG-2. 

SC-39 Improvements in IFF Mark IV. 

SC-45 Antenna system for long-range AvSV (LRASV). 

SC-46 Antenna system for use with S-band lightweight ASV. Now' X-band LWASV. Extension to include consultant on 

procurement. See AC-234.01. Extension to cut-off low-altitude thirty-inch scanner. 

SC-50 Lightweight responder beacon equipment to work with Rebecca, AN/APB-1, or similar equipment. Superseded 
by SC-63. 

SC-51 Aircraft interception system AI-3. 

SC-52 Aircraft gun laying X-band automatic tracking set, AGL-2; advisor. 

SC-53 Instrument landing; ground control of landing system, GCA. Consultant to Army and advisor on production at 
Gilfillan. Extended to advisor on production at FT & R. See AC-236.04. 

SC-54 Microwave racons. Superseded by SC-63. 

SC-55 Detection set, range only RO-1. 

SC-56 Long range navigation by means of pulse transmission, Loran. Consultant on construction of Loran receivers, 
AN/APN-9, at RCA cancelled. Extended to procurement^of TG Loran. Not extended to direct reading indicator 
receiver. For extension to LF Loran see AN-18. See AC-236.01. 

SC-57 Airborne range-only radar equipment, ARO; Consultant on AN /APG-14. Procurement of 120 Units of AN /APG-13. 
See AC-235.01. 

SC-58 Tail warning equipment for bombers, TWS-1, TWS-2. 

SC-59 Tail warning equipment for fighter aircraft, FTW. 

SC-60 Microwave early warning set, MEW and construction of 5; consultant on 21.04 to -8 procurement. Construction 
of one additional unit; construction of three more units with other items. Extended to beacon modification kits 
for AN/CPS-IA. See AC-234.04. 



159 


SERVICE PROJECT NUMBERS (Continued) 


Service 


Project 


Number 

Subject 


SC-61 

SC-62 

SC-62.01 

SC-62.02 

SC-62.03 

SC-62.04 

SC-62.05 

SC-62.06 

SC-62.07 

SC-62.08 

SC-62.09 

SC-62.10 

SC-62.11 

SC-62.12 

SC-63 


SC-63.01 

SC-63.02 

SC-63.03 

SC-63.04 

SC-63.05 


SC-63.06 

SC-66 

SC-68 

SC-69 

SC-71 

SC-72 

SC-73 

SC-74 

SC-75 

SC-76 

SC-77 

SC-80 

SC-82 

SC-89 

SC-94.23 

SC-101 

SC-lOl.Ql 

SC-101.02 

SC-101.03 

SC-102 

SC-103 

C-104 

SC-106 


Army Projects (Continued) 

Fire control for cannon in XA-26B. See AC-35. 

Trainers for radar equipments. 

Consultant for trainer for AN/APQ-5 (RC-217), LAB. Number changed to AC-262.01. 

Consultant for bench trainer SCR-520 (RC-225). 

Consultant for beacon simulator for RC-225-T-1. 

Consultant for Link trainer for SCR-520/720. 

Consultant for trainer for SCR-617. 

Consultant for trainer for SCR-519-T3. 

Consultant for crew trainer for SCR-702. Amended to cover a universal AGL Trainer for AN /APG-1, 3, 8, 15 and 16. 
Consultant for optical projection trainer. 

Trainer for H2X, interim model and supersonic type. Extension to procurement. Number changed to AC-262.09. 
Eagle trainer AN/APQ-7-T1 with procurement of 8. Extended to procurement of 50. Number changed to AC-262.10. 
Development of trainer AN/APG-15-T1. Procurement of 30. Number changed to AC-262.11. 

Procurement of Falcon trainers. Number changed to AC-262.12. 

Racons; this directive incorporates previously accepted projects SC-50 and SC-54. For subdivision see SC-63.01- 
63.05. 

AN/CPN-3, AN/CPN-5 (BGS). 

AN/CPN-8 (BPS). See AC-263.02. 

AN/CPN-6 (BGX). See AC-263.03. 

AN/UPN-1, 2, formerly AN/PPN4, AN/PPN-5 (BUPS). Includes consultant service on procurement. See AC- 
263.04. 

AN/UPN-3, 4, formerly AN/PPN-6, AN/PPN-7 (BUPX). Extension includes consultant service on procurement. 
See AC-263.05. 

Development of K-band beacons. See AC-263.06. • 

Proposed interim blind bombing equipments against land targets, based on SCR-717T3 components. Withheld 
until commitments on ASG were completed, then accepted. 

X-band attachment for long range ASV. 

Airborne gun sight; AGS. Consultant services on AN/APG-15. See AC-235.02. 

SCR-615. Height finder for GCI. See AC-239.01. 

Consultant service on air transportable ground controlled approach equipment, AN/CPN-4. See AC-236.05. 
Methods for elimination of ground clutter. Extended to procurement of 2 MTI kits for SCR-584 and consultant 
on MC-642. Extended to improved search- type antenna. 

Development of the V-beam GCI equipment. Extended to procurement. Extended to consultant on AN /CPS-6A. 

Extended to procurement of six beacon modification kits. See AC-239.05. 

'‘Beavertail” height finder to use with LREW and consultant to Army on its manufacture, AN /CPS-4. See AC-239.03. 
S-band Oboe equipment “Aspen,” with consultant and procurement service. 

Improvement in Mark III, IFF. Extended to modification of SCR-695, SCR-729. IFF for ground radar kept; 
for airborne see AC-233.01. 

Radar range finder for toss bombing. Advisor. See AC-235.03. 

Advisor on dark-trace console. 

Advisor on radar for T-38 Director. 

Development of CW magnetron for Division 15. 

Development work and consultant service on SCR-584. (Formerly carried under SC-6.) Extended to procurement 
of N2 gate and X-band kit; extended to procurement of 8 MTI kits, MC-642. 

Consultant service on plotting table equipment, RC-294. See AC-233.03. 

Consultant service on search antenna for SCR-584. 

Consultant service on sector scans for SCR-584; MC-645. 

Consultant on SCR-702A, B, AN/APG-1, 2. (Formerly carried under SC-6.) 

Advisor service for AN/APG-3, 16. See AC-235.04. , 

Dielectric consultation and tests. 

Test equipment. Subdivided into 106.01-106.05. 


160 


SERVICE PROJECT NUMBERS {Continued) 


Service 


Project 


Number 

Subject 


SC-106.01 

SC-106.02 

SC-106.03 

SC-106.04 

SC-106.05 

SC-106.06 

SC-107 

SC-109 

SC-115 

SC-119 

SC-143 

SC-144 

SC-145 

SC-146 

SC-148 


Army Projects (Continued) 

Consultant on TS-125/AP power meter. See AC-237.01. 

Consultant on RF-3A/AP phantom target. 

Consultant on AS-15/AP antenna. 

Consultant on production of directional transmission line coupler for AN/APQ-13. Extension to AN/APS-15 
accepted. See AC-237.04. 

Consultant on test equipment TS-155/UP. 

K-band test equipment, TS-253 (dummy load), TS-254 (power meter); extended to TS-259 (XA-) /AP. Formerly 
TTK-IRL. 

AN/TPS-10 ‘‘Little Abner.” Extended to procurement. See AC-239.04. 

Air-transportable Loran. Extended to procurement. Extended to advisor on production at Bendix. See AC-236.02. 
Reduced titanium compounds for use as resistors. 

IFF for AGL, AGS and AI. See AC-233.01. 

Radar for automatic weapons. Not accepted, except for advisor service if needed. 

Radar mortar locator. Not accepted, except for advisor service if needed. 

Forward combat area detector. Not accepted, except for advisor service if needed. 

Field artillery radar, 2 kits for SCR-584 modification. 

High dielectric ceramics, low temperature-coefficient ceramics, piezoelectric crystals. 


Advisory and Consultant Services by the Radiation Laboratory 


These are in addition to the ones previously listed under AN-3, -7, -21; NA-109, -129, -181, -182, -184; NO-115, -155, -172; 
NR-103; NS-101, -108, -118, -119, -133, -149, -153, -156, -162,^169, -171, -174, -175, -190, -196, -223. -224, -227, -228, -229, 
-232, -265, -268, -272, -285, -286, -296, -299, -314, -319, -331, -351, -357; AC-1; SC-37, -46, -53, -56, -57, -60, -62, -63, -63.05, 
-72, -75, -76, -80, -82, -89, -101, -102, -103, -106. 


AIA 

AN/APN-4 

AN/APN-6 (BAS) ) 

AN/CPN-8 (BPS) ) 

AN/APQ-13 

AN/APS-1 

AN/APS-3A 

AN/APS-6 

AN/APS-19 

AN/ARR-17, ART-18 

AN/MPN-1 


AN/PPN-3 

AN/TPS-IB 

ARO 

ARO 

ASD Equipment 
ASG, ASD, AIA 
Trainers 
Block V 
Bomb Director 
DG Synchro Lmit 
Echo Box 
Echo Box 
FM Radar 

Loran 

Mark 1 and 
Mark 11 
Mark 19 


Advisor to the Navy on production of AIA equipment. 

Advisor to the Army on production of AN/APN-4 by Philco. 

Consulting service to the Army on Galvin beacon production. 

Advisor to the Army for AN/APQ-13; H2X (WE). 

Consultant to the Army on development of AN/APS-1. 

Advisor to the Navy for production at Sperry of AN/APS-3A. 

Advisor for construction of AN/APS-6. 

Advisor to the Navy on AN/APS-19. 

Advisor to Navy on AN/ARR-17, ART-18 at Philco. 

Advisor to the Navy on all developments in connection with the “talk-down” radio equipment 
AN/MPN-1. 

Advisor to the Navy on j)roduction by Airadio. 

Advisor to Bureau of Ships on MTI application. 

Advisor on lightweight ARO, at Philco. 

Advisor on FM ARO, at Raytheon. 

Advisor to the Navy on ASD production at Sperry. 

Consultant to the Navy on the development of ASG, ASD and AIA trainers. 

Advisor to Bureau of Aeronautics on Block V Relay Radar Transmitter. 

Advisor to Bureau of Ordnance on Bomb Director MK2 Mod 0, formerly Mark 22. 

Advi.sor to the Navy on “DG” Synchro LTnit. 

Advisor to Navy on WE production of X-band echo box. 

Advisor on TS-218/UP, TS-219/UP. 

Advisor to the Navy on the RCA contract for the development of components and systems using the 
FM i:)rinciple. 

Advi.sor to Navy on production of equipments. 

Advisor to the Navy on target designation transmitter Mark 11 and gun director control unit Mark 1. 

Advisor to the Navy on the use of radar equipment Mark 19 with gun director Mark 49. Division 7 
has the responsibility for the redesign of gun director Mark 49. 


161 


SERVICE PROJECT NUMBERS {Continued) 


Service 

Project 

Number 

✓ 

Subject 

Photography 

Radar Beacons 
Relay Radar 
SCR-615B 

SG 

SG-3 

SN 

SO- 11 Antenna 
SO-12 

SO-12M 

SQ 

SRB 

su 

TS-148/UP 

VF 

YK Racons 

Advisory and Corisultant Senrices by the Radiation Laboratory (Continued) 

Advisor to the Navy on radar scope idiotography. 

Mk 2, Mods 0 and 1. Consultant service to the Navy. 

Advisor for ground relay radar for Marine Corps. 

Consultant to the Army on production of SCR-615B. Extension of SC-71. 

Advisor to the Navy on SG. 

Advisor to the Navy on SG-3. 

Advisor to the Navy on SN. 

Advisor to the Navy on SO-11 Antenna 

Advisor to the Navy on MTI for SO-12. 

Advisor to the Navy on SO-12M. 

Consultant to the Navy on the construction of the indicators of SQ; advisor on other components of SQ. 
Advisor to the Navy on BTL development of SRB. 

Advisor to the Navy on SU. 

Advisor to Navy on these test sets built by WEM Co. 

Consultant to the Navy on Raytheon production of VF (formerly P31). 

Advisor to the Navy on the development of the model YK series of racon equipment by Philco. Con- 
sultant on production of TS- 155/UP. Liaison on application of beacon development under SC-63 
to glide and power driven bombs accepted. 


162 




INDEX 


The subject indexes of all STR volumes are combined in a master index printed in a separate volume. For 
access to the index volume consult the Army or Navy Agency listed on the reverse of the half-title page. 


ABL-15, British radio research unit, 20 
Absorbing materials, radar 
see Radar-absorbing materials 
Ad Hoc Committee on Instrument 
Landing, 71 

AEW (airborne early warning) radar, 89 
AGL (airborne gunlaying) radar, 80 
AGS (airborne gunsight) radar, 82-83 
AI (aircraft interception) radar, 27-28 
AIA fighter plane radar, 52 
AIA-1 improved radar (AN/APS-6), 52 
Air Defense Research] and Development 
Establishment (ADRDE), 18 
Airborne early warning (AEW) radar, 
89 

Airborne fire control with microwave 
radar, 11 

Airborne gunlaying (AGL) radar, 80-81 
AGL-1, -2, -3; 80 
field applications, 81 
historical resume, 44 
Airborne gunsight (AGS) radar, 82-83 
AGS Mark I and Mark II, 82 
AN/APG-15 development, 82 
Airborne moving-target indication 
(AMTI), 96 

Airborne range-only (ARO) radar, 81-83 
Aircraft interception (AI) radar, 42-43 
AI Mark II, 27 
AI Mark IV, 27-28 
antisubmarine use, 6 
British and American features com- 
bined, 43 

experimental systems, 4-5 
project initiated, 3-4 
SCR-517; 43 
SCR-520; 42-43 
SCR-720; 10, 42-43 
Aircraft radar systems, 71-84 

airborne gunlaying (AGL) radar, 80-8 1 
airborne gunsight (AGS) radar, 82-83 
airborne range-only (ARO), 81-83 
blind bombing at sea, 78-80 
Eagle, high resolution radar, 75-78 
early developments, 34-35 
ground control of aircraft landing 
(GCL), 72-73 

lighthouse transmitter-receiver sys- 
tem, 81-83 

low-voltage magnetron systems, 84 
navigational and bombing radars, 
74-75 

pulse-glide-path (PGP), 71-72 
talk down systems, 72-74 
Aircraft-to-surface vessel radar 
see ASV radar 

Altitude line on radar scope, reduced 
by HARP, 135-136 
AMTI (airborne moving-target indi- 
cation), 96 

AN/APG-13A, Falcon radar, 83 


AN/APG-13B, Vulture radar, 83 
AN/APG-15, conical scan radar, 82 
AN /APQ-5, blind bombing radar, 78-80 
AN/APQ-7, Eagle radar, 76-77 
AN/APS-3, bombing radar, 53 
AN/APS-6, search radar, 52 
AN/APS-10, search radar, 84 
AN/ APS- 14, relay link, 89 
AN/APS-15, navigation radar, 74 
AN/APS-20, early warning radar, 90 
AN/ARC-18, relay transmitter, 91 
AN/ART-22, relay transmitter, 91 
AN/ARW-35, relay receiver, 91 
AN/CPS-4, heightfinder, 68 
AN/CPS-6, beacon, 68-69 
AN/FPG-1, coastal defense radar, 67 
Anisotropic electrical properties, 
HARP, 106 

AN/MPG-1, mobile coastal radar, 67 
Antenna pattern distortions reduced by 
HARP 

see HARP correction of detrimental 
reflection 

Antenna pattern fluctuations, 135 
Antenna radiation reduced with HARP 
screen, 135-137 

altitude line on radar scope reduced, 
135-136 

cross coupling between antennas re- 
duced, 136 

test equipment tuned without radi- 
ation, 136-137 
Antenna scanning, 43-45 
airborne gunlaying radar, 44 
automatic scanning and tracking, 
44-45 

conical scanning, 43 
range circuits, 44 
Antennas 

design development, 40 
fixed antennas, 75-76 
MEW (microwave early warning), 64 
scanning antenna, 76 
Schwarzschild antenna, 67 
3 foot scanning antenna, 75 
Antiaircraft fire control, microwave 
radar, 12 

airborne gunlaying (AGL) radar, 
80-81 

airborne gunsight (AGS) radar, 82-83 
AN/TPG-1, mobile coastal radar, 67 
AN/TPS-10, mountainous country 
radar, 69-70 

Army’s collaboration with MIT-RL, 
16-17 

ARO (airborne range-only) radar, 81-82 
ASV radar, 46-49 
ASV Mark II, 27 
B-18 installation, 47-48 
blimp equipment development, 48-49 
bomber experience, 47-48 


British development, 27-28 
field trials, 47 

patrol bomber (ASD-1) radar, 53 
preliminary tests, 46-47 
3 cm. development, 52-53 
torpedo bomber (ASD) radar, 53 
submarine warfare use^ 6 
Attenuation in resonant-absorbing lay- 
ers, 112 

Australian radar research group, 21 
Automatic tracking, 44-45 
first unit, 5 
SCR-584; 45 
XT-1 unit, 44-45 

B tube magnetron, 57 
B-18’s ASV installations, 47-48 
Baffle covered with HARP, 134 
BBRL (British branch, MIT-RL) 
blind bombing introduced, 20 
development, 19-20 
European warfare, 8 
French invasion role, 20 
personnel sent to Pacific, 8 
role of technical civilian scientists, 21 
Beacons, 11 

Beavertail height-finder, AN/CPS-4; 

68 

BFR (blind-flying) radar, 84 
Binders for HARP, 101-102 
Blimps installed with radar, 48-49 
Blind bombing, 11 
Blind bombing at high altitudes 
see Eagle, high resolution radar 
Blind bombing at sea, 78-80 
antishipping attacks, 79-80 
antishipping technique, 79 
Pacific performance, 78-80 
project initiation, 78 
snooper squadrons, 79 
Blind-flying radar (BFR), 84 
Blind-landing radar (PGP), 71-72 
Bomb bay doors covered with HARP, 
135 

Bombers equipped with ASV radar, 
47-48 

Bombing through overcast (BTO) 
see Eagle, high resolution radar 
Brewster’s angle 

determined in resonant-absorbing 
layer theory, 113 

• for materials of high refractive index, 
112 

British Admiralty Signal Establish- 
ment, 18 

British collaboration with MIT-RL, 
17-19 

British prewar work on radar, 26 
British Technical Mission, 3, 31-32 
B-tube magnetron, 57 
Buoys identified by HARP, 133 


163 


164 


INDEX 


C tube magnetron, 57 
Cadillac project, 89-96 
organization, 90 
project’s origin, 89 
purpose of the project, 89 
Cadillac I system, 90-95 

airborne system components, 90-91 
coordination of airborne and ship- 
board systems, 91 
experimental systems, 91-92 
flight testing, 92 
Navy trials, 94-95 
performance data, 95 
reorganization of project, 94 
shipboard system components, 91 
Cadillac I system, production, 92-94 
delivery scheduling, 93 
design changes, 93 
instruction manuals, 94 
maintenance program, 94 
organization, 92-93 
performance testing, 93 
production scheduling, 93 
type testing, 93 
Cadillac II system, 95-96 
applications, 96 
design, 95 

development and production, 95-96 
initiation of program, 95 
Camouflage of targets by HARP 
see HARP camouflage of targets 
Cavity magnetron, 3, 29 
CIC (combat information center) 
bombers equipped with CIC, 95-96 
Cadillac I shipboard system, 91 
Coastal defense radar, 66-67 
AN/FPG-1; 67 
AN/TPG-1; 67 
early installations, 46 
need for radar coastal defense, 66-67 
SCR-598 design, 67 
Coaxial line 

electromagnetic measurements of 
HARP, 106-108 

resonant layers, measuring apparatus, 
115 

terminations, 137 
transmission, 41 

Columbia Radiation Laboratory 
(CUDWR-RL), 55-62 
one centimeter magnetron project, 
55-59 

organization, 56 

tunable 3-cm magnetron project, 
59-62 

Conducting flakes, HARP, 100-101 
Conical scanning, 43-45 

airborne gunlaying radar, 44 
experimental systems, 44 
SCR-584 unit, 45 
theory of operation, 43 
XT-1 mobile unit, 45 
Consoles, SCI, 86 

Continuous-wave applications, 29-30 
Coupling between antennas reduced by 
HARP, 136 

“Crown of Thorns”, magnetron tube, 60 
C-tube magnetron, 57 


CXAM, shipboard aircraft search sys- 
tem, 26-27 

CXBL system, ground control of inter- 
ception, 63 

CXHR system, ship control of inter- 
ception, 85-87 
design, 85 

operational characteristics, 85 
production, 86-87 
requirements, 85 

Demagnetizing factor, suspended par- 
ticles, 99 

Depolarizing factor, suspended par- 
ticles, 99 ' 

DeVilbiss spraying machine, used in 
HARP production, 103 
Dielectric constant material 
see HARP 

Diffracted radar radiation, 130-131 
Diffraction, microwaves, 9-10 
Diffraction, not correctable by HARP, 
135 

Director console design, SCI, 86 
Dumbo I and II, ASV equipment, 47 
Dunnington’s analyzer for Sambo, 

131 

E-5 magnetron tube, 58 
Eagle, high resolution radar, 75-78 
computer, 76 
field application, 78 
fixed antenna experiments, 75-76 
flight tests’ results, 76 
Mark I design, 76 

Mark I modifications and applica- 
tions, 77 

requirements of high-altitude blind 
bombing device, 75 
scanning antenna development, 76 
training and test programs, 77-78 
Universal bombsight, 76 
Echo strength, factor in radar target 
camouflage, 129 

Electromagnetic measurements, HARP 
samples, 106-108 
accuracy of measurements, 108 
coaxial line propagation, 106-107 
rectangular wave guide propagation, 
107-108 

Electromagnetic properties, HARP, 
105-106 

anistropic properties, 106 
dielectric constant, 105-106 
electric field, 105-106 
electric induction, 105-106 
magnetic field, 105-106 
magnetic induction, 105 
magnetic permeability, 105-106 
Maxwell’s equations, 105-106 
Electrostatically deflected indicator 
tubes, 41 

Falcon, airborne range-only adaption, 
83 

Ferromagnetic metals in HARP flakes, 
101 



I 


Filter center, reception of information 
reported by MEW, 65 
Filters of HARP material 

see HARP film transmission filters 
Fire-control radar for shore batteries, 
66-67 

AN/FPG-1; 67 
AN/TPG-1; 67 

need for radar, coastal defense, 66-67 
SCR-598 design, 67 

GCA (ground control of aircraft ap- 
proach), 73-74 
field performance, 73-74 
HARP used to eliminate reflection, 
134 

Mark II system, 73-74 
GCL (ground control of aircraft land- 
ing), 72-73 

“Ghosts” produced on PPI, 133-134 
Graphite, HARP flakes material, 101 
Grazing angles, 118 
Ground control, aircraft approach 
(GCA), 73-74 
field performance, 73-74 
HARP used to eliminate reflection, 
134 

Mark II system, 73-74 
Ground control, aircraft landing (GCL), 
72-73 

Ground control of interception, 63-64 
CXBL system, 63 

high-power radar requirements, 63 
SCR-615 model, 63 
Ground force operations with micro- 
wave radar, 12 

Ground systems projects, MIT-RL, 
63-70 

beavertail height-finder, 68 
fire-control radar for shore batteries, 
66-67 

high-power radar, ground control of 
interception, 63-64 
lightweight height-finding radar, 
69-70 

MEW, 64-66 
V-beam system, 68-69 
GR-S artificial rubber, HARP binder 
use, 101 

Gun fire-control system Mark 56, 87-88 
function and operation, 87 
origin, 87 

production and application, 87-88 
Gunlaying system, airborne, 80-81 
AGL models, 80-81 
field applications, 81 
historical resume, 44 

H system, radar beacons, 11 
H 2 S navigational radar system, 74-75 
H-iX navigational radar system, 11, 
74-75 

Harbor radar installations, 46 
HARP, electromagnetic properties, 105- 
108 

anisotropic properties, 106 
dielectric constant, 105-106 
electric field, 105-106 



INDEX 


165 


electric induction, 105-100 
electromagnetic measurements on 
thin samples, 106-108 
magnetic field, 105-106 
magnetic induction, 105 
magnetic permeability, 105-106 
MaxAvell’s equations, 105-106 
propagation in a dielectric and per- 
meable medium, 105-106 
HARP, fabrication process, 100-104 
binders, 101-102 
classes of processes, 102 
conducting flakes, 100-101 
essential elements of fabrication, 100 
knifing technique, 102-103 
low-index HARP production, 103 
pilot plant production, 103-104 
refractive indices, 102 
spraying technique, 103 
HARP, historical survey, 99 
HARP, physical concept, 99-100 
basic concept, 99 

calculation of electric and magnetic 
susceptibilities, 100 
depolarizing factor, 99 
electromagnetic behavior, 100 
suspended magnetic particles con- 
cept, 99 

HARP, technical applications, 129-138 
identification of radar target, 131-133 
laboratory uses, 138 
radar antenna interference correc- 
tion, 133-135 

screening and test equipment, 135- 
137 

terminations, 137-138 
HARP, theory 

see Radar-absorbing materials 
HARP camouflage of targets, 129-131 
broad band HARP, 131 
broad band HARP film, 130 
character of radar target, 129 
echo strength of target, 129 
narrowband HARP, 130-131 
radar cross section, 129 
return radiation from target, 130 
Schnorkel breathing tubes of German 
U-boats, camouflage, 130 
^ shape of target determines success of 
camouflage, 129-130 
HARP correction of detrimental re- 
flection, 133-135 
baffle covered with HARP, 134 
bomb bay doors covered with HARP, 
135 

mast reflections reduced, 134 
metallic parts of antenna covered, 134 
reflections from neighboring struc- 
tures screened, 134 
shadow region diffraction, unaffected 
by HARP, 135 

side lobes in antenna pattern reduced, 
133-134 

HARP film transmission filters, 121-124 
band width of filter, 123-124 
materials with high refractive index, 
122 

maximum transmission, 123-124 


transmission as wave length func- 
tion, 122 

transmission exj^eri mentally meas- 
ured, 123-124 
very thin film, 122 
wave length dependence of trans- 
mission, 122 

HARP identification of targets, 131-133 
basic concept, 131 

buoys and navigational aids identi- 
fied, 133 

Harpoon system, 133 
modulation, 131-132 
noise factor, 131-132 
Sambo system, 132-133 
time necessary for indication of 
modulation, 132 

HARP reduction of antenna radiation, 
135-137 

altitude line on radar scope reduced, 
135-136 

cross coupling between antennas re- 
duced, 136 

test equipment tuned without radi- 
ation, 136-137 

Harpoon system of target identifica- 
tion, 131, 133^ 

Height-finding radar, 68-70 
beavertail, AN/CPS-4; 68 
lightweight unit, AN/TPS-10; 69-70 
V-beam system, 68-69 
High resolution radar 

see Eagle, high resolution radar 
History of radar activities 

see Radar activities, history and or- 
ganization 

Hobbing process, magnetron construc- 
tion, 58 

H 2 S navigational radar system, 74-75 
H 2 X navigational radar system, 11, 
74-75 

I-f problems in receiver design, 40 
IFF, Cadillac I system, 91 
Index of refraction, HARP, 102 
Indicator problems of MEW, 65 
Indicator tubes, 41-42 
electrostatically deflected tubes, 41 
long persistence tubes, 41 
PPI indicators, 42 
standard tubes, 42 

Interrogator-responsor (IFF), AN/ 
APX-13; 91 

Kamikaze attacks, illustrate need for 
radar search beyond horizon, 89 
Kinjiro Okabe’s magnetron work, 29 
Klystron 

construction and operation, 28 
radiation source, 30 

L-115, pressure sensitive adhesive, 102 
L series, magnetron tuning tubes, 60-62 
LAB, low altitude blind bombing at 
sea, 78-80 

antishipping attacks, 79-80 
antishii)ping technique, 79 


Pacific performance, 78-80 
project initiation, 78 
snooper squadrons, *79 
Laboratory equipment utilizing HARP, 
138 

Lamination of HARP to produce non- 
directional film, 126-127 
Lawson's receiver for detecting modu- 
lation, 131 

Lighthouse transmitter-receiver 
(LHTR) systems, 81-83 
airborne gunsight (AGS), 82-83 
airborne range-only (ARO), 81-82 
Loomis, Alfred A. 

see Radar activities, history and or- 
ganization 

Loran (long range navigation), 49-51 
Atlantic use, 8 
development, 49-50 
early organization, 4 
experimental models tested, 50 
low-frequency Loran, 51 
navigational aid, 51 
Pacific use, 8 

skywave synchronization, 50 
station network installations, 50 
theory, 49 

Lorenz-Lorentz formula, 100 
Low-voltage magnetron radar (AN/ 
APS- 10), 84 

Magnetic properties, HARP 
see Electromagnetic properties, 
HARP 
Magnetrons 

cavity magnetron, 29 
development in j\IIT-RL, 40 
produced in U.S., 31-32 
split-anode magnetron, 28-29 
tubes, 57-58 

tunable 3-cm magnetron, 59-62 
tunable 10-cm magnetron, 60 
Magnetrons on 1 centimeter, 55-62 
design and specifications develop- 
ment, 57-58 
earliest studies, 55 
extended facilities, 55-56 
organization problems, 55 
rising sun magnetron, 59 
strapped tube designs, 58-59 
Mark 56 gun fire-control system, 87-88 
function and operation, 87 
origin of system, 87 
production and application, 87-88 
Massachusetts Institute of Technology, 
Radiation Laboratory 
see MIT-RL 

Mast antenna reflections, reduced by 
HARP, 134 
Maxwell’s equations 

applied to propagation in a dielectric 
and permeable medium, 105-106 
applied to theory of resonant-absorb- 
ing layers, 109-115 

MEW (microwave early warning), 64- 
66 

antenna, 64 

control of intercei^ting figliters, 12 


166 


INDEX 


elevation of installation increased, 65 
experimental experience, 65 
field operations, 65-66 
first installation, 64 
indicator problems, 65 
mobile system, 66 
power requirement problems, 64 
required conditions for adequate pro- 
tection, 64 
versatility, 8 

Microwave Committee, 3-4, 32-33 
Microwave radar, airborne applica- 
tions, 10-11 

airborne fire control, 11 
aircraft interception, 10 
beacons, 11 
blind bombing, 11 
navigation, 11 
surface vessel search, 11 
Microwave radar, ground based ap- 
plications, 12-13 
aircraft landing, 13 
antiaircraft fire control, 12 
control of air operations, 12-13 
control of intercepting fighters, 12 
early warning of approaching air- 
planes, 12 

ground force operations, 12 
Microwave radar, sea applications, 13, 
45-49 

airborne systems, ASV, 46-49 
fighter control, 13 
fire control, 13 
shipborne systems, 46 
surface surveillance, 13 
Microwaves, 9-13, 28-30 
see also Radar activities, history and 
organization 
advantages, 9 
cavity magnetron, 29 
continuous-wave applications, 29-30 
diffraction, 9-10 
interference, 9 
Klystron, 28 

split-anode magnetron, 28 
versatility of application, 10 
waveguides, 29 
MIT-RL, 13-24, 33-54 
see also Radar activities, history and 
organization 

airborne system development, 34-35 
collaboration with Army and Navy, 
16-17 

collaboration with manufacturers, 
15-16, 53-54 

collaboration with the British, 17-19 
divisional structure, 14-15 
early development, 25-26 
first experimental system, 34 
ground systems projects, 63-70 
Microwave Committee establishes 
laboratory, 3-4, 32-33 
MIT administration, 14 
organization, 13-15 
personnel, 22-23 
personnel recruited, 33 
sectional divisions, 33-34 
MIT-RL field service, 19-22 


Australian research group, 21 
BBRL, British unit, 19-22 
communications’ system, 22 
domestic field service, 19 
PB-OSRD radar group, 21 
Pearl Harbor research group, 21 
MIT-RL technical program, 39-54 
aircraft interference project, 42-43 
component parts of radar sets de- 
veloped, 39-42 

fire control and automatic tracking 
project, 43-45 

improvement of component parts, 
radar sets, 39-42 
Loran project, 49-51 
microwave radar over water, 45-49 
radar on three centimeters, 51-54 
Modulation, 131-132 
noise level, 132 

propeller modulation, effect on Sam- 
bo, 132-133 

receiver for modulation detection, 131 
signal to noise ratio, 131-132 
subharmonic frequencies produced 
by HARP applications, 131, 132 
Mountainous country radar, AN /TPS- 
10, 69-70 

NAB (navigational aid to bombing), 
74-75 

early development, 74 
H 2 S British system, 74-75 
HjX, improved NAB, 74-75 
Navigation, long-range 
see Loran 

Navigational aids identified by HARP, 
133 

Navy’s collaboration with MIT-RL, 
16-17 

NDRC Division 14 development, 25-26 
Neoprene, HARP binder use, 101-102 

“Oboe” system, radar beacons, 11 
Organic polymers in HARP binders, 101 

Particle parameters, 101 
Patrol bomber (ASD-1) radar develop- 
ment, 53 

PB-OSRD radar group, 21 
Permeability 

effect on HARP electromagnetic be- 
havior, 100 

in preparation of HARP conducting 
flakes, 101 

resonant absorbing layers, 116 
PGC (portable ground control of inter- 
ception), 68-69 

PGP (pulse-glide-path) aircraft radar, 
71-72 

Pilot plant production, HARP, 103-104 
elements, 103 
Navy specification, 104 
})lant’s capacity, 104 
spraying process, 103-104 
Pliobond rubber cement, 101 
Polarization in absorbent layers, 113-115 
parallel and perpendicular polariza- 
tion compared, 113-115 


polarization in plane of incidence, 113 
polarization perpendicular to plane 
of incidence, 113 

Portable ground control of intercep- 
tion (PGC), 68-69 
PPI (plan position indicators) 

Cadillac I system, 91 
first airborne set, 5 
“ghost” echoes produced by reflec- 
tions, 133-134 
tube development, 42 
Propagation in a dielectric and per- 
meable medium, 105-106 
anisotropic electrical properties, 106 
effect of metal flakes in HARP ma- 
terials, 106 
field quantities, 105 
in homogeneous media, 105 
isotropic medium propagation, 105 
Maxwell’s equations, 105-106 
propagation vector components, 106 
Propeller blades treated with HARP 
see Sambo system 
Pseudo-Sambo effects, 132 
Pterodactyl, airborne range-only adap- 
tion, 83 

Pulse modulator development, 40 
Pulse-forming network, 40 
Pulse-glide-path (PGP) aircraft radar, 
71-72 

Radar activities, history and organiza- 
tion, 3-24 

microwave survey, 9-13 
MIT-RL, 3-4, 13-24 

1940, early work, 4 

1941, exploration, 4-6 

1942, emergence from laboratory, 
6-7 

1943, engineering and production, 7-8 

1944, field service, 8 

1945, termination of project, 8-9 
radar division of NDRC, 25-26, 30-31 

Radar before 1940; 26-28 
British developments, 26 
British developments in field use, 
27-28 

CXAM, Navy’s earliest radar, 26-27 
SCR-270 and 271, Army’s earliest 
radar, 26-27 

Radar on 3 centimeters, 51-54 
AIA-1 bomber system (AN/APS-6), 
52 

AIA fighter system, 52 
AN/APS-3 development and pro- 
duction, 53-54 
early objectivesj 51 
early trials, 51 

patrol bomber (ASD-1) radar, 53 
torpedo bomber (ASD) radar, 53 
Radar sets, development of component 
parts, 39-42 
antenna design, 40 
indicator tubes, 41-42 
magnetron, 40 
pulse modulator, 40 
receiver design, r-f and i-f problems, 
40-41 


INDEX 


167 


synchronizer unit, 39, 42 
Radar targets camouflaged 

see HARP camouflage of targets 
Radar targets identified by HARP 
see HARP identification of targets 
Radar-absorbing materials, 109-128 
see also HARP, electromagnetic prop- 
erties 

behavior of waves in open space, 
109-114 

coaxial line, 114 

conditions for complete absorption, 

no 

determination of phase of reflected 
waves, 110-112 

perpendicular and parallel polariza- 
tion compared, 113-115 
])olarization in plane of incidence, 113 
polarization perpendicular to plane 
of incidence, 113 
waveguide, 114 • 

Radar-absorbing materials, experimen- 
tal data, 115-121 
angles of incidence, 117-118 
curved surfaces, 120-121 
cuts across HARP film, 119 
diffracted radiation, 120 
directional film, 120-121 
measurements at grazing angles, 118 
measurements in closed space, 115 
measuring apparatus, 115 
permeability, 116 
phase of reflected wave, 118 
temperature variations, 117 
Radar-absorbing materials, nonhomo- 
geneous, 124-128 

cross lamination of HARP to pro- 
duce nondirectional film, 126-127 
dielectric and conducting layers al- 
ternated, 127 

general discussion, 124-126 
HARP films interleaved with paper, 
128 

thin layer interposition, 126 
Radial strapped tube magnetrons, 59 
Radiation reduction with HARP screen, 
135-137 

altitude line on radar scope, reduc- 
tion, 135-136 

cross coupling between antennas, re- 
duction, 136 

test equipment tuned Avithout radi- 
ation, 136-137 

Radiation returned from radar target, 
130 

Receiver design problems, 40-41 
i-f use, 40 

r-f receiver detector, 41 
TR-box problems, 41 
waveguide transmission lines, 41 
Reflections detrimental to radar opera- 
tion corrected by HARP 
see HARP correction of detrimental 
reflection 
Refractive index 
HARP, 102 

magnetic materials, 117 
Relaxation time for magnetization, 105 


Resnatron, multi-element vacuum tube, 
31 

R-f co-axial lines, 41 
R-f problems in receiver design, 41 
Rising sun magnetron, 59 
Rubber cement, HARP binder use, 
101-102 



CXHR system,^ 
dire 


^^^ion, 85-87 

rmo^ 

fetai 


Is, 85 

aiy of 


re' 


Sambo system, target identification, 
131-133 

advantages, 133 
analyzer, 131 
basic principle, 132 
HARP applied to propeller blades, 
131 


Defe 


nr console design, 86 
!pe^ gojrgg||rception con- 

SCI model, 86 



3111 Mark 56; 

shij) control of interception, 85-87 
Shipboard system, Cadillac I, 91 
Shore battery radar, 66-67 


propeller modulation, 132-133 
pseudo-Sambo effects, 132-133 
spinner covering on hub, 132 
subharmonic frequencies generated, 
132 

Schnorkel breathing tubes of German 
IT-boats, camouflaged, 130 
Schwarzschild antenna, SCR-598; 67 
SCI (ship control of interception) sys- 
tem, 85-87 
design, 85 

operational characteristics, 85 
production, 86-87 
requirements, 85 

SCR-268, mobile fire control radar, 27 
SCR-270, mobile, early warning radar, 
12, 26-27 

SCR-271, fixed early warning radar, 
26-27 

SCR-517, search radar, 43, 48 
SCR-520, aircraft interception radar, 43 
SCR-582, fixed coastal radar, 46 
SCR-584, mobile search radar, 44-45 
operation, 12 

performance in the field, 45 
XT-1 prototype, 45 
SCR-598, coastal defense radar, 66-67 
SCR-615, ground control of intercep- 
tion radar, 12, 63 

SCR-717, surface vessel detection radar. 


AN/FPG-1; 67 
AN/TPG-1; 67 

need for radar in coastal defense, 
66-67 

SCR-598 design, 67 
Side lobes in antenna pattern reduced 
by HARP, 133-134 
Skywave synchronization of Loran, 
50-51 

SM sets, ship radar, 13 
Snooper squadrons, 79 
SP sets, ship radar, 13 
Specularly reflected radiation, 130-131 
Split-anode magnetron, 28-29 
SSAG (sea-search-attack group), 48 
Station network installations, Loran, 50 
Strapped tube magnetrons, 58-59 
Subharmonic frequencies generated 
with HARP, 132 

Submarine detection with ASV radar, 
48 

Surface surveillance with microwave 
radar, 13 

Surface vessel search, 11 
Suspended magnetic particles 
see HARP 

SX system, shij) control of intercep- 
tion, 13, 86-87 
Synchronizer unit, 42 


11,48 

SCR-720, search radar 

aircraft interception use, 10 
development and production, 42-43 
HARP used to eliminate “pull”, 134 
Screening covered with HARP, 135- 
137 

altitude line on radar scope reduced, 
135-136 

cross coupling between antennas re- 
duced, 136 

test equipment tuned without radi- 
ation, 136-137 

Sea-search-attack group (SSAG), 48 
Selective transmission filters of HARP 
film 

see HARP film transmission filters 
SG, ship search radar systems, 46 
SG-1 installations aboard destroyers. 


Talk down, aircraft landing system, 
72-74 

field performance, 73-74 
HARP used for reflection elimination, 
134 

Mark I experimental system, 72-73 
Mark II system, early tests and im- 
provements, 73 
preliminary investigation, 72 
Targets camouflaged by HARP 
see HARP camouflage of targets 
Targets identified by HARP 

see HARP identification of targets 
Terminations constructed of HARP, 
137-138 

coaxial terminations, 137 
construction process, 137 
effect of wavelength on a termination, 
137 


134 

Shadow region diffraction, not correct- 
able by HARP, 135 
Ship aircraft search system, 26-27 


quarter wave absorption theory, 137 
X-band wave guide terminations, 137 
Test equipment treated with HARP, 
136-137 


S kCKET~^ 


168 


INDEX 


Torpedo bomber (ASD) radar develop- 
ment, 53 

Tracking automatically, 44-45 
first unit, 5 
SCR-584; 45 
XT-1 unit, 44-45 
Traffic control radar 
MEW system, 64-66 
V-beam system, 68-69 
Transmission filters of HARP film 
see HARP film transmission filters 
Transmit-receive (TR) box, 34, 41 
TRE (British Telecommunications Re- 
search Establishment), 18-19 
Tunable 3-cm magnetron, 59-62 
‘'Crown of Thorns”, 60 
experimental L-2 tuning tubes, 60-61 


L series, tuning tubes, 61-62 
10-cm tunable magnetron, forerun- 
ner, 60 

tuning experiments, 60 

Tuning, test equipment treated with 
HARP, 136-137 

Universal bombsight (UBS) program, 
76 

University of Birmingham’s cavity 
magnetron, 3 

University of California’s resnatron 
development, 31 

V-beam early warning system, 68-69 

Vulture (airborne range-only radar 
adaption), 83 




Waveguide 

microwaves, 29 

resonant layers, measuring appa- 
ratus, 115 

transmission lines, 41 
used in electromagnetic measure- 
ments of HARP samples, 106- 
108 

X-band waveguide terminations, 137 
XASD, torpedo bomber radar, 53-54 
XT-1 automatic tracking unit, 44-45 
early design’s excellence, 5 
SCR-584 prototype, 45 
tracking of high speed targets, 45 
use in experiments, 45 


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PropBfty of Tochnicol Roports Soction 

SCIENCE AND TECHNOLOGY DIVISION 


Library of Congress 


DECLASSIFTRn 
By authority Secretary of 

SEP 2 6 I960 

Defense memo 2 August 1960 
UBRABY OF CONGRESS 







